Bistable Compliant Four-Bar Mechanisms With a Single Torsional Spring

Significant reduction in cost and time of bistable mechanism design can be achieved by understanding their bistable behavior. This paper presents bistable compliant mechanisms whose pseudo-rigid-body models (PRBM) are four-bar mechanisms with a torsional spring. Stable and unstable equilibrium positions are calculated for such four-bar mechanisms, defining their bistable behavior for all possible permutations of torsional spring locations. Finite Element Analysis (FEA) and simulation is used to illustrate the bistable behavior of a compliant mechanism with a straight compliant member, using stored energy plots. These results, along with the four-bar and the compliant mechanism information, can then be used to design a bistable compliant mechanism to meet specified requirements.

Elastic Averaging in Flexure Mechanisms: A Muliti-Beam Parallelogram Flexure Case-Study

Over-constraint is an important concern in mechanism design because it can lead to a loss in desired mobility. In distributed-compliance flexure mechanisms, this problem is alleviated due to the phenomenon of elastic averaging, thus enabling performance-enhancing geometric arrangements that are otherwise unrealizable. The principle of elastic averaging is illustrated in this paper by means of a multi-beam parallelogram flexure mechanism. In a lumped-compliance configuration, this mechanism is prone to over-constraint in the presence of nominal manufacturing and assembly errors. However, with an increasing degree of distributed-compliance, the mechanism is shown to become more tolerant to such geometric imperfections. The nonlinear load-stiffening and elasto-kinematic effects in the constituent beams have an important role to play in the over-constraint and elastic averaging characteristics of this mechanism. Therefore, a parametric model that incorporates these nonlinearities is utilized in predicting the influence of a representative geometric imperfection on the primary motion stiffness of the mechanism. The proposed model utilizes a beam generalization so that varying degrees of distributed compliance are captured using a single geometric parameter.

A Simple Method for Inverse Kinematic Analysis of the General 6R Serial Robot

Because the solution to inverse kinematics problem of the general 5R serial robot is unique and its assembly condition has been derived, a simple effective method for inverse kinematics problem of general 6R serial robot or forward kinematics problem of general 7R single-loop mechanism is presented based on one-dimension searching algorithm. The new method has the following features: (1) Using one-dimension searching algorithm, all the real inverse kinematic solutions are obtained and it has higher computing efficiency; (2) Compared with algebraic method, it has evidently reduced the difficulty of deducing formulas. The principle of the new method can be generalized to kinematic analysis of parallel mechanisms.

An Objective Evaluation of Displacement-Amplifying Compliant Mechanisms for Sensor Applications

Displacement-amplifying compliant mechanisms (DaCMs) reported in literature are mostly used for actuator applications. This paper considers them for sensor applications that rely on displacement measurement, and evaluates them objectively. The main goal is to increase the sensitivity under constraints imposed by several secondary requirements and practical constraints. A spring-mass-lever model that effectively captures the addition of a DaCM to a sensor is used in comparing eight DaCMs. We observe that they significantly differ in performance criteria such as geometric advantage, stiffness, natural frequency, mode amplification, factor of safety against failure, cross-axis stiffness, etc., but none excel in all. Thus, a combined figure of merit is proposed using which the most suitable DaCM could be selected for a sensor application. A case-study of a micro machined capacitive accelerometer and another case-study of a vision-based force sensor are included to illustrate the general evaluation and selection procedure of DaCMs with specific applications. Some other insights gained with the analysis presented here were the optimum size-scale for a DaCM, the effect on its natural frequency, limits on its stiffness, and working range of the sensor.

Design and Fabrication of an Elastic Knee Orthosis: Preliminary Results

When humans hop or run on compliant surfaces they alter the stiffness of their legs so that the overall stiffness of the leg-surface system remains the same. Adding a spring in parallel to the ankle joint incites a similar neuromuscular response; humans decrease their biological ankle stiffness such that the overall ankle stiffness remains unchanged. These results suggest that an elastic exoskeleton could be effective at reducing the metabolic cost of locomotion. To further increase our understanding of human response we have developed an elastic knee brace that adds a stiff spring in parallel to the knee. It will be used as a test platform in ascertaining the neuromuscular effects of adding a parallel knee spring while hopping on one leg. This paper focuses primarily on the mechanical design and implementation of our elastic knee orthosis. Results of the forthcoming studies of human subjects wearing this knee orthosis will be presented in a separate article that will focus on the biomechanics and the neuromuscular adaptations of the human body. Prior research found that the neuromuscular response to hopping on compliant surfaces was the same when running on compliant surfaces. We expect that our results from hopping with springs in parallel with the knee will also be applicable to running. This elastic knee brace represents the first phase of an ongoing research project to develop a passive compliant lower-body exoskeleton to assist in human running. It is expected that this research will benefit healthy individuals as well as those with disabilities causing decreased muscle function.

Representation of the Variable Chain Mechanisms With Sequential Movement

A mechanism that encounters a certain change in the number of links or degree of freedom during operation will also result the variation of the topological structure in every stage. Since the mechanisms with variable chain in different stages during operation have different topologies, but the applications of this kind of mechanisms are very extensively. And this also result the complications of representation of the topology thoroughly. Mechanisms with variable chain now always been represented by graph according to the topology of each stage, but hardly represent by using a formula. We would like to propose an approach to develop the function for representing the mechanism with variable chain that focus on the sequential movement, and help the representation of the operation not only by the graph but also by the function. According to the operation of the mechanisms with variable chain, the movement of the mechanisms can be classified into parallel system movement and sequential system movement. Parallel movement mechanisms are the mechanisms operate more than one links in the same time when giving an input; and when we give an input that can operate just only one link and effect and transfer the movement of the next one step by step, we can call this kind of mechanisms as sequential mechanisms. In this work we apply composite function for represent the movement of each stage, and also verified the representation by applying it on the existed examples.

Spherical Bistable Micromechanism

A new micromechanism, the Spherical Bistable Micromechanism (SBM), is described. The SBM has several advantageous features, which include: two stable positions that require power only in transitioning from one to the other; robustness against small disturbances; and an output link with a stable out-of-plane orientation. The SBM may be useful in applications such as 2-D optical mirror arrays or in erecting out-of-plane structures.

A Characterization of Cam Transmissions Through an Identification of Lumped Parameters

In this paper, a numerical-experimental procedure is proposed for an identification of parameters in cam transmissions. Models with lumped parameters are defined specifically for cam transmissions. Experimental tests are carried out on main components of a cam transmission in order to estimate the values of mass, damping and stiffness lumped parameters through a low-cost easy-operation procedure. Experimental tests are also carried out in order to characterize the dynamic behaviour of a whole cam transmission. A comparison of numerical and experimental results is used in order to calibrate the values of lumped parameters. Experimental tests have been carried out by means of suitable test-beds for cams that have been built specifically at University of Brescia and at LARM in Cassino as alternative testing solutions.

Towards Uniformly Distributed Compliance in Compliant Mechanisms: A Multi-Objective Approach

Researchers in the field of optimal synthesis of compliant mechanisms have been working to develop tools that yield distributed compliant devices to perform specific tasks. However, it has been demonstrated in the literature that much of this work has resulted in mechanisms that localize compliance rather than distribute it as desired. In fact, Yin and Ananthasuresh (2003) [1] demonstrate that based on the current formulation of optimality criteria and analysis via the finite element (FE) technique, a lumped compliant device will always exist as the minimizing solution to the objective function. The addition of constraints on allowable strain simply moves the solution back from this objective. Therefore, modification to the standard optimality criteria needs to take place. Yin and Ananthasuresh [1] proposed and compared several approaches that include distributivity-based measures within the optimality criteria, and demonstrated the effectiveness of this approach. In this paper, the authors propose to build on this problem. In a similar manner, a general approach to the topology synthesis problem will be suggested to yield mechanisms in which the compliance is distributed throughout the device. This work will be based on the idea of including compliance distribution directly within the objective functions, while addressing some of the potential limiting factors in past approaches. The technique will be generalized to allow simple addition of criteria in the future, and to deliver optimal designs through to manufacture. This work will first revisit and propose several quantitative definitions for distributed compliant devices. Then, a multi-objective formulation based on a non-dominating sort and Pareto set method will be incorporated that will provide information on the nature of the problem and compatibility of employed objective functions.

Modeling Uncertainty for Planar Meso-Scale Manipulation and Assembly

While robotic assembly at the centimeter and meter length scale is well understood and is routine in the manufacturing industry, robotic grasping and manipulation for meso-scale assembly at the millimeter and sub-millimeter length scales are much more difficult. This paper explores an possible way to manipulate and assemble planar parts using a micro-manipulator with a single probe capable of pushing parts on a planar surface with visual feedback. Specifically, we describe a study of the uncertainty associated with planar surface friction with a goal of developing a model of manipulation primitives that can be used for assembly. We describe a series of experiments and data analysis algorithms that allow us to identify the main system parameters for quasi-static operation, including the friction coefficient and the force distribution, while characterizing the uncertainty associated with these parameters. This allows us to bound the range of motions resulting from the uncertainty, which is necessary to design robust open-loop meso-scale manipulation and assembly motion plans.