Design and Analysis of a Monolithic Compliant Dwell Mechanism

A novel, monolithic flexible translational dwell mechanism that is driven by a DC motor is designed in this study. Mechanism consists of an initially straight, large deflecting pinned-pinned buckling beam as a coupler, semi-circular compliant arc as a follower, rigid crank and a slider. An approximate dwell motion is created since the slider doesn’t move until the critical buckling load of the flexible coupler is achieved and then snaps to its maximum displacement by pushing the follower arc beam. As the maximum bending on the arc is reached, slider moves back to its initial as the crank follows a full rotation. Dynamical lumped model of the mechanism is obtained by integrating first and second kind of elliptic integral solution of pinned-pinned beam with polynomial formulation method. Optimal dimensions and geometric positions are explored using commercially available FEA program (ADAMs). Mechanism is built by 3D printing the entire mechanism as a single piece using polyethylene terephthalate glycol (PETG). Mathematical model of the mechanism is validated through experimental setup and ADAMs simulations.

Optimization of a Snap Through Spring for a Hydraulic Valve With Hysteresis Response Behavior

The hydraulic binary counter requires switching valves with a hysteretic response. In this paper an elastic snap through element is studied as means for that. The concept is based on a buckling beam which is elastically supported in axial direction in order to adjust its buckling properties with moderate manufacturing precision and to assure a well defined snap through behavior. The elastic support is provided by a cantilever beam. A rigorous optimization is performed heading for a most compact and fatigue durable design which exhibits the required lateral force displacement characteristics. A genetic algorithm is used to find the global design optimum. The stress/displacement properties of each design variant are computed by a compact model of the snap through system. It is derived by a Ritz method to obtain approximate solutions of the nonlinear buckling beam behavior. Its validity is checked by a Finite Element model. A compact design is possible if high strength spring steel is used for the elastic elements.

Design of Translational and Rotational Bistable Actuators Based on Dielectric Elastomer

Dielectric elastomer (DE), as a group of electro-active polymers, has been widely used in soft robotics due to its inherent flexibility and large induced deformation. As sustained high voltage is needed to maintain the deformation of DE, it may result in electric breakdown for a long-period actuation. Inspired by the bistable mechanism which has two stable equilibrium positions and can stay at one of them without energy consumption, two bistable dielectric elastomer actuators (DEAs) including a translational actuator and a rotational actuator are proposed. Both the bistable actuators consist of a double conical DEA and a buckling beam and can switch between two stable positions with voltage. In this paper, the analytical models of the bulking beam and the conical DEA are presented first, and then the design method is demonstrated in terms of force equilibrium and moment equilibrium principle. The experiments of the translational bistable DEA and the rotational bistable DEA are conducted, which show that the design method of the bistable DEA is effective.

A Buckling Flexure-Based Force-Limiting Mechanism

A force-limiting buckling flexure has been created which can be used in a wide array of applications where excessive force from an implement can cause harm or damage. The buckling flexure is monolithic, contains no electronics, and can be manufactured using a single shot in an injection molding machine, making it extremely cost effective. In this paper, the design of this flexure is applied to a force-limiting toothbrush as an example of how this buckling flexure may be applied in a real-world technology. An overview of the buckling flexure is presented, and a structural model is shown to predict when the flexure will elastically buckle. This model is compared to data collected from flexures fabricated with varying buckling beam thickness. The data show that the force to buckle the flexure when applied at the tip can be predicted to within 20.84%. Furthermore, a preliminary model is presented which enables design of the buckling beam’s displacement, such that the total breakaway deformation can be maximized, making sensing the sudden deformation easier. As part of the application of the buckling flexure, an ergonomic, injection moldable toothbrush was created with the flexure built into the neck of the brush. When the user applies too much force while brushing, the flexure gives way and alerts the user when they have applied too much force and when the user lets off the force, the brush snaps back to its original shape. This design methodology is generalized and can be utilized in other force limited applications where an injection moldable, pre-set force, purely mechanical breakaway device is desired.