A Dynamic Model of Magneto-Active Elastomer Actuation of the Waterbomb Base

Of special interest in the growing field of origami engineering is self-folding, wherein a material is able to fold itself in response to an applied field. In order to simulate the effect of active materials on an origami-inspired design, a dynamic model is needed. Ideally, the model would be an aid in determining how much active material is needed and where it should be placed to actuate the model to the desired position. A dynamic model of the origami waterbomb base, a well-known and foundational origami structure, is developed using Adams, a commercial dynamics software package. Creases are approximated as torsion springs with stiffness and damping. The stiffness of an origami crease is calculated, and the dynamic model is verified using the bistability of the waterbomb. An approximation of the torque produced by magneto-active elastomers (MAE) is calculated and is used to simulate MAE-actuated self-folding of the waterbomb.

Improving Techniques in Statically Equivalent Serial Chain Modeling for Center of Mass Estimation

Any articulated system of rigid bodies defines a Statically Equivalent Serial Chain (SESC). The SESC is a virtual chain that terminates at the center of mass (CoM) of the original system of bodies. A SESC may be generated experimentally without knowing the mass, CoM, or length of each link in the system given that its joint angles and overall CoM may be measured. This paper presents three developments toward recognizing the SESC as a practical modeling technique. Two of the three developments improve utilizing the technique in practical applications where the arrangement of the joints impacts the derivation of the SESC. The final development provides insight into the number of poses needed to create a usable SESC in the presence of data collection errors. First, modifications to a matrix necessary in computing the SESC are proposed. Second, the problem of generating a SESC experimentally when the system of bodies includes a mass fixed in the ground frame are presented and a remedy is proposed for humanoid-like systems. Third, an investigation of the error of the experimental SESC versus the number of data readings collected in the presence of errors in joint readings and CoM data is conducted. By conducting the method on three different systems with various levels of data error, a general form of the function for estimating the error of the experimental SESC is proposed.

On the Comparison of the Dynamic Performance of Open-Loop and Closed-Loop Mechanisms

In general, mechanical systems with closed-loop mechanisms can achieve significantly higher operating speeds as compared to open-loop mechanisms such as robots performing identical tasks. In this brief paper, the reason for the superior dynamic performance of closed-loop mechanisms as compared to open-loop mechanisms performing identical tasks is shown to be the inherent dynamic response limitations of the actuation devices in open-loop dynamic systems. Several examples are provided.

Gyroscope-Free Link Parameter Measurement Using Accelerometers and Magnetometer

Knowledge of joint angles, angular velocities is essential for control of link mechanisms and robots. The estimation of joint angles and angular velocity is performed using combination of inertial sensors (accelerometers and gyroscopes) which are contactless and flexible at point of application. Different estimation techniques are used to fuse data from different inertial sensors. Bio-inspired sensors using symmetrically placed multiple inertial sensors are capable of instantaneously measuring joint parameters (joint angle, angular velocities and angular acceleration) without use of any estimation techniques. Calibration of inertial sensors is easier and more reliable for accelerometers as compared to gyroscopes. The research presents gyroscope-less, multiple accelerometer and magnetometer based sensors capable of measuring (not estimating) joint parameters. The contribution of the improved sensor are four-fold. Firstly, the inertial sensors are devoid of symmetry constraint unlike the previously researched bio-inspired sensors. However, the accelerometer are non-coplanarly placed. Secondly, the accelerometer-magnetometer combination sensor allows for calculation of a unique rotation matrix between two link joined by any kind of joint. Thirdly, the sensors are easier to calibrate as they consist only of accelerometers. Finally, the sensors allow for calculation of angular velocity and angular acceleration without use of gyroscopes.

A Unified Kinetostatic Analysis Framework for Planar Compliant and Rigid Body Mechanisms

Although many dynamic solvers are available for planar mechanisms, there is no readily accessible static solver that can be used in analysis of planar mechanisms with elastic components which achieve motion utilizing deformation of elastic members. New simulation tools are necessary to better understand the compliant mechanisms and to increase their usage in daily life. This framework was developed to fill this gap in planar mechanism design and analysis. The framework was written in MATLAB and is capable of kinematic and static analysis of planar mechanisms with compliant joints or links. Detailed information on implementation of the code is presented and is followed by the capabilities of the framework. Finally, the simulation results were compared with the Adams software to test the validity of the framework.

Defining Exercise Motions Using a Segment-Joint Kinematic Model: Part I — Problem Formulation and Methodology

Extensive research in exercise, a subcategory of physical activity, has been conducted with the aim of instructing the individual in the proper techniques when performing specific aerobic and anaerobic forms of exercise. This past research, however, does not answer the basic question of how to specify an exercise motion mathematically. This is the first part of a two-part paper that presents a new approach to defining specific exercise motions by using a segment-joint model of the human body. This model makes use of kinematic equations used in robotics and visually represents various exercise motions using a 3-D virtual reality human manikin. In this first part of the paper, we introduce the segment-joint model and how this is utilized in combination with a systematic methodology in order to define specific exercise motions. Part II is concerned with providing a complete validation of the proposed segment-joint model approach.

Kinetostatic Performance Analysis of a Redundantly Driven Parallel Kinematic Manipulator

In general the mechanical handling of objects in space is performed by manipulators, whose number of actuators is consistent with the number of required degrees of freedom. In addition, manipulators can be equipped with redundant drives, providing the manipulator with more actuators than the mobility actually requires. Thus, an active distribution of drive torques is enabled. Accordingly, this research intends to analyze the effects of torque distribution in over-actuated manipulators relating to load-optimized and energy-efficient handling. By developing torque distribution strategies the maximum torque levels can be reduced and the required drive power thus be decreased. This results in an increased drive utilization, which improves the energy-efficiency of the handling system. On this basis, an innovative handling concept is analyzed, which represents an over-determined system given the number of actuators. Hence, it is shown that the drive utilization of manipulators can be significantly improved by means of actuation redundancy. For this purpose different mathematical optimization approaches are analyzed, which solve the over-actuated system with defined optimization targets. Here, the optimal torque distribution is found using an algorithm, which minimizes the maximum torque for each object position. The results demonstrate the efficiency of active torque distribution in terms of over-actuated manipulators. For a further approach it is planned to develop control methods including optimized torque distribution strategies in order to improve the performance and the energy efficiency of the entire manipulator.

Determination of Variable Stiffness of a Human Elbow for Human-Robot Interaction

This paper aims to emulate human motion with a robot for the purpose of improving human-robot interaction (HRI). In order to engineer a robot that demonstrates functionally similar motion to humans, aspects of human motion such as variable stiffness must be captured. This paper successfully determined the variable stiffness humans use in the context of a 1 DOF disturbance rejection task by optimizing a time-varying stiffness parameter to experimental data in the context of a neuro-motor Simulink model. The significant improved agreement between the model and the experimental data in the disturbance rejection task after the addition of variable stiffness demonstrates how important variable stiffness is to creating a model of human motion. To enable a robot to emulate this motion, a predictive stiffness model was developed that attempts to reproduce the stiffness that a human would use in a given situation. The predictive stiffness model successfully decreases the error between the neuro-motor model and the experimental data when compared to the neuro-motor model with a constant stiffness value.

Designing Optimal Origami Structures by Computational Evolutionary Embryogeny

As the advantages of foldable or deployable structures are being discovered, research into origami engineering has attracted more focus from both artists and engineers. With the aid of modern computer techniques, some computational origami design methods have been developed. Most of these methods focus on the problem of origami crease pattern design — the problem of determining a crease pattern to realize a specified origami final shape, but don’t provide computational solutions to actually developing a shape that meets some design performance criteria. This paper presents a design method that includes the computational design of the finished shape as well as the crease pattern. The origami shape will be designed to satisfy geometric, functional, and foldability requirements. This design method is named computational evolutionary embryogeny for optimal origami design (CEEFOOD), which is an extension of the genetic algorithm (GA) and an original computational evolutionary embryogeny (CEE). Unlike existing origami crease pattern design methods that adopt deductive logic, CEEFOOD implements an abductive approach to progressively evolve an optimal design. This paper presents how CEEFOOD — as a member of the GA family — determines the genetic representation (genotype) of candidate solutions, the formulation of the objective function, and the design of evolutionary operators. This paper gives an origami design problem, which has requirements on the folded-state profile, position of center of mass, and number of creases. Several solutions derived by CEEFOOD are listed and compared to highlight the effectiveness of this abductive design method.

Origami Folding and Bar Frameworks

One of the more computationally demanding tasks in a process of synthesizing “from scratch” origami crease patterns designed for a given purpose involve a simulation capability to track the progression of the folding process as the pattern folds. This work presents an approach to simulate origami folding based on bar frameworks. The work is related to joint frameworks and projected polyhedral, as they apply to folding. The analysis starts from a representation of a crease pattern as an undirected graph G(E,V) formed by edges E and vertices V. A framework G(p) is an instance of G where the vertex locations are assigned positions according to a vector valued function p(t), where t marks the folding progression and t=0 represents the initial, flat configuration. The strategy presented is based on finding a sequence of instances {p(1), p(2), …} corresponding to an analytic flex p, i.e., functions such that edges in all G(p(t)) have the same length. The method is based on using a finite element description of a bar framework corresponding to a truss-like structure congruent with G(p). Solutions to an eigenvalue problem associated with this structure provide the means to update from p(t) to p(t+1). Two simple (purely geometric) optimization problems adjust the update to compensate for higher order effects, guaranteeing that the length of the edges remain constant. The methodology can be used to achieve configurations close to “flat folding”, provided that no interference of the faces occurs along the way. We expected that physically-motivated constraints (stresses, deformations, etc.) and sensitivity analysis computations will be more easily represented in this framework and therefore this formulation will have an advantage over more standard “origami mathematics” approaches. The approach is illustrated with an example of folding a simple 10-crease pattern.