Shrinkable Self-Similar Structure Design

Origami techniques, as folding and unfolding, can be utilized in shrinkable structures. Especially when the crease pattern is rigid foldable, it can be treated as a mechanical linkage of rigid panels connected by hinges. Since rigid foldable crease patterns have the strong geometrical constraint of the facets not being able to stretch or bend, it is difficult to design new crease patterns, and variations of existing patterns are limited. However, it is known that there are cases where crease patterns can be made rigid foldable by adding some slits. This paper proposes a mechanical linkage that folds into a similar flat shape by adding slits. A method is presented of generating rigid foldable crease patterns in arbitrary polygons that fold smaller, and it is confirmed that structures that have a mechanism for shrinking can be generated from these crease patterns by using rigid thick panels and hinges.

A portable six-wheeled mobile robot with reconfigurable body and self-adaptable obstacle-climbing mechanisms

Mobile robots can replace rescuers in rescue and detection missions in complex and unstructured environments and draw the interest of many researchers. This paper presents a novel six-wheeled mobile robot with a reconfigurable body and self-adaptable obstacle-climbing mechanisms, which can reconfigure itself to three locomotion states to realize the advantages of terrain adaptability, obstacle crossing ability and portability. Design criteria and mechanical design of the proposed mobile robot are firstly presented, based on which the geometry of the robot is modelled and the geometric constraint, static conditions and motion stability condition for obstacle crossing of the robot are derived and formulated. Numerical simulations are then conducted to verify the geometric passing capability, static passing capability and motion stability and find feasible structure parameters of the robot in obstacle crossing. Further, a physical prototype of the proposed mobile robot is developed and integrated with mechatronic systems and remote control. Using the prototype, field experiments are carried out to verify the feasibility of the proposed design and theoretical derivations. The results show that the proposed mobile robot satisfies all the criteria set and is feasible for applications in disastrous rescuing scenarios.

Triple Crossed Flexure Pivot Based on a Zero Parasitic Center Shift Kinematic Design

Thanks to their absence of play, absence of contact friction and possible monolithic fabrication, flexure pivots offer advantages over traditional bearings in small-scale, high accuracy applications and environments where lubrication and wear debris are proscribed. However, they typically present a parasitic center shift that deteriorates their rotational guidance accuracy. Existing solutions addressing this issue have the drawbacks of reducing angular stroke, prohibiting planar design, or introducing overconstraints or underconstraints. This article introduces a new triple crossed flexure pivot called TRIVOT that has a reduced parasitic center shift without overconstraints nor internal mobility, while allowing either optimal stress distribution in the flexures or a planar design. The new architecture also makes it possible to place the center of rotation outside of the physical structure, which is not the case with traditional bearings. Based on finite element simulations, we show that the parasitic shift is reduced by one order of magnitude in comparison to the widely used crossed flexure pivot. We also derive and validate formulas for the rotational stiffness and angular stroke limit of the TRIVOT. Finally, we show that a high support stiffness can be achieved with a lowest uwanted eignenfrequency 13.5 times higher than the first eigenfrequency. We expect this new pivot to become a competitive alternative to the crossed flexure pivot for applications where high accuracy and compactness are required.

Design of a non circular gear Mechanism with Twice Unequal Amplitude Transmission Ratio

This study proposes a new non–circular gear transmission mechanism with an involute–cycloid composite tooth profile to realize the twice unequal amplitude transmission (In a complete rotation cycle of gear transmission, instantaneous transmission ratio has twice fluctuations obvious with unequal amplitude) of non–circular gears. The twice unequal amplitude transmission ratio curve was designed based on Fourier and polynomial functions, the change law of the Fourier coefficient on the instantaneous transmission ratio(In non-circular gear transmission, the transmission ratio changes with time, and the transmission ratio of non-circular gear should be instantaneous transmission ratio) was analyzed, and the pressure angle and contact ratio of the involute–cycloid composite tooth profile was calculated. The involute–cycloid composite tooth profile non–circular gear was machined by WEDM technology, while its meshing experiment was performed using high-speed camera technology. The results demonstrate that the instantaneous transmission ratio curve value obtained via the high-speed camera experiment was consistent with the simulation value of virtual software. Furthermore, the involute–cycloid composite tooth profile was applied in the seedling pickup mechanism of non–circular gear planetary gear train. The possibility of the application of the involute–cycloid composite tooth profile in the seedling pickup mechanism was verified by comparing the consistency of the theoretical and simulated seedling picking trajectory.

The Mixed-Body Model: A Method for Predicting Large Deflections in Stepped Cantilever Beams

This paper presents a method for predicting endpoint coordinates, stress, and force to deflect stepped cantilever beams under large deflections. This method, the Mixed-Body Model or MBM, combines small deflection theory and the Pseudo-Rigid-Body Model for large deflections. To analyze the efficacy of the model, the MBM is compared to a model that assumes the first step in the beam to be rigid, to finite element analysis, and to the numerical boundary value solution over a large sample set of loading conditions, geometries, and material properties. The model was also compared to physical prototypes. In all cases, the MBM agrees well with expected values. Optimization of the MBM parameters yielded increased agreement, leading to average errors of <0.01 to 3%. The model provides a simple, quick solution with minimal error that can be particularly helpful in design.

Algorithmic Selection of Preferred Grasp Poses using Manipulability Ellipsoid Forms

An algorithm to search for a kinematically desired robotic grasp pose with rolling contacts is presented. A manipulability measure is defined to characterise the grasp for multi-fingered robotic handling. The methodology can be used to search for the goal grasp pose with a manipulability ellipsoid close to the desired one. The proposed algorithm is modified to perform rolling based relocation under kinematic constraints of the robotic fingertips. The search for the optimal grasp pose and the improvement of the grasp pose by relocation is based on the reduction of the geodesic distance between the current and the target manipulability matrices. The algorithm also derives paths of the fingertip on the object surface in order to achieve the goal pose. An algorithmic option for the process of searching for a suitable grasp configuration is hence achieved.

Novel Methodology for Inflection Circle based synthesis of Straight Line Crank Rocker Mechanism

Emerging fields like Compact Compliant Mechanisms have created newer/novel situations for application of straight line mechanisms. Many of these situations in Automation and Robotics are multidisciplinary in nature. Application Engineers from these domains are many times uninitiated in involved procedures of synthesis of mechanisms and related concepts of Path Curvature Theory. This paper proposes a predominantly graphical approach using properties of Inflection Circle to synthesize a crank rocker mechanism for tracing a coupler curve which includes the targeted straight line path. The generated approximate straight line path has acceptable deviation in length, orientation and extent of approximate nature well within the permissible ranges. Generation of multiple choices for the link geometry is unique to this method. To ease the selection, a trained Artificial Neural Network (ANN) is developed to indicate relative length of various options generated. Using studied unique properties of Inflection Circles a methodology for anticipating the orientation of the straight path vis-à-vis the targeted path is also included. Two straight line paths are targeted for two different crank rockers. Compared to the existing practice of selecting the mechanism with some compromise due to inherent granularity of the data in Atlases, proposed methodology helps in indicating the possibility of completing the dimensional synthesis. The case in which the solution is possible, the developed solution is well within the design specifications and is without a compromise.

A numerically stable algorithm for analytic inverse kinematics of 7-DoF S-R-S manipulators with joint limit avoidance

This paper presents a numerically stable algorithm for analytic inverse kinematics of 7-DoF S-R-S manipulators with joint limit avoidance. The arm angle is used to represent the self-motion manifold within a global arm configuration. The joint limits are analytically mapped to the arm angle space for joint limit avoidance. To profile the relation between the joint angle and arm angle, it is critical to characterize the singular arm angle for each joint. In the-state-of-the art methods, the existence of the singular arm angle is triggered by comparing a discriminant with zero given a threshold. We will show this leads to numerical issues since the threshold is inconsistent among different target poses, leading to incorrect range of the arm angle. These issues are overcome by associating indeterminate joint angles of tangent joints with angles of 0 or pi of cosine joints, rather than using an independent threshold for each joint. The closed-form algorithm in C++ code to perform numerically stable inverse kinematics of 7-DoF S-R-S manipulators with global arm configuration control and joint limit avoidance is also given.

A family of novel compliant linear-motion mechanisms based on compliant rolling-contact element pivot

Compliant linear-motion mechanisms are of great use in precision machines, due to their excellent performances such as infinite resolution and low cost. The accuracy of the mechanisms is an important consideration for mechanical design in applications, especially in the case of large working load. Considering that COmpliant Rolling-contact Element (CORE) pivot is characterized with high bearing capacity, the paper adopts it as a building block to design a family of compliant linear-motion mechanisms for applications of heavy load. These mechanisms are achieved by replacing four rigid pivots in a parallel four-bar mechanism with CORE pivots, and the motion accuracy is improved by means of contacting surfaces design of four CORE pivots. Firstly, structures of CORE pivot are introduced and five extended arrangements for bearing heavy load are presented. Meanwhile, motion for the CORE pivot is analyzed and preconditions for achieving a pure roll are discussed. Then, configuration of the compliant linear-motion mechanisms constructed by CORE pivots is obtained, and kinematics of the mechanisms is analyzed and parametric design condition for rectilinear motion is modeled. Based on the condition, detailed topological structures of the mechanisms are designed. Finally, motion simulations and experiment tests are implemented to verify accuracy of the proposed mechanisms. The results demonstrate that the mechanisms proposed in this paper are capable of offering a high-precision linear motion and providing a promising application prospect in precision machines.

TOWARDS THE DESIGN OF KRESLING TOWER ORIGAMI AS A COMPLIANT BUILDING BLOCK

In this paper, the use of the Kresling tower origami as a building block for compliant mechanism design is considered. Design tools to help building systems using this origami are introduced. First, a model which can describe the tower kinematics during its deployment is introduced. This model is exploited to link the origami pattern geometry to the main Kresling tower characteristics which include the position of stable configurations, the helical motion and the configuration of panels during the tower deployment. Second, a local modification of fold geometry is introduced to adjust the tower stiffness. This aims at modifying the actuation force without affecting the kinematics and consists in the removal of material on the fold line where constraints are concentrated during the folding. Experimental evaluation is conducted to verify the relevance of the proposed models and the impact of fold line modification. As a result, the design relationships derived from the model are precise enough for the synthesis, with a global relative mean error around 0.8% for the prediction of the helical motion, and 3.1% for the assessment of stable configurations. The capacity to significantly modify the actuation force thanks to the fold line modification is also observed with a reduction of about 73% of the maximal force to switch between two stable configurations.