Brian P. Trease

Design of Large-Displacement Compliant Joints

Flexure joints are widely used to approximate the function of traditional mechanical joints, while offering the benefits of high precision, long life, and ease of manufacture. This paper investigates and catalogs the drawbacks of typical flexure connectors and presents several new designs for highlyeffective, kinematically-behaved compliant joints. A revolute and a translational compliant joint are proposed (Figure 1), both of which offer great improvements over existing flexures in the qualities of (1) large range of motion, (2) minimal axis drift, (3) increased off-axis stiffness, and (4) reduced stressconcentrations. Analytic stiffness equations are developed for each joint and parametric computer models are used to verify their superior stiffness properties. A catalog of design charts based on the parametric models is also presented, allowing for rapid sizing of the joints for custom performance. Finally, two multi-degree-of-freedom joints are proposed as modifications to the revolute joint. These include a compliant universal joint and a compliant spherical joint, both designed to provide high degrees of compliance in the desired direction of motion and high stiffness in other directions.

Accommodating Thickness in Origami-Based Deployable Arrays

The purpose of this work is to create deployment systems with a large ratio of stowed-to-deployed diameter. Deployment from a compact form to a final flat state can be achieved through origami-inspired folding of panels. There are many models capable of this motion when folded in a material with negligible thickness; however, when the application requires the folding of thick, rigid panels, attention must be paid to the effect of material thickness not only on the final folded state, but also during the folding motion (i.e., the panels must not be required to flex to attain the final folded form). The objective is to develop new methods for deployment from a compact folded form to a large circular array (or other final form). This paper describes a mathematical model for modifying the pattern to accommodate material thickness in the context of the design, modeling, and testing of a deployable system inspired by an origami six-sided flasher model. The model is demonstrated in hardware as a 1/20th scale prototype of a deployable solar array for space applications. The resulting prototype has a ratio of stowed-to-deployed diameter of 9.2 (or 1.25 m deployed outer diameter to 0.136 m stowed outer diameter). INTRODUCTION The purpose of this work is to develop deployment systems that unfold from a compact form to a large array. This work ∗Corresponding author: lhowell@byu.edu is motivated by the need for compactly folded solar arrays for space applications. A large ratio of stowed-to-deployed diameter enables large solar arrays to be launched in their compact, folded configuration and then deployed in space to a much larger surface area. For our objectives, a design with synchronous deployment was desired to simplify actuation and deployment. Deployment from a compact form to a final flat state can be achieved through origami-inspired folding of panels. There are many models capable of this motion when folded in paper or other materials with negligible thickness; however, when the application requires the folding of thick, rigid panels, material thickness can inhibit the folding motion. To be rigid-foldable, the panels must not be required to flex to attain the final folded form. This paper describes the approach for modifying the design of an origami six-sided flasher model to accommodate material thickness. This work builds on existing models to present a unique design that is rigid-foldable through two different methods. In the first method, the panels are allowed to flex along their diagonals. In the second method, the panels are affixed to a flexible membrane with discrete gap spacing between the panels. Both folding solutions enable the model to be rigid-foldable.

Design and Application of Compliant Mechanisms for Surgical Tools

This paper introduces the benefits of exploiting elasticity in the engineering design of surgical tools, in general, and of minimally invasive procedures, in particular. Compliant mechanisms are jointless mechanisms that rely on elastic deformation to transmit forces and motion. The lack of traditional joints in these single-piece flexible structures offers many benefits, including the absence of wear debris, pinch points, crevices, and lubrication. Such systems are particularly amenable to embedded sensing for haptic feedback and embedded actuation with active-material actuators. The paper provides an overview of design synthesis methods developed at the Compliant Systems Design Laboratory and focuses specifically on surgical applications. Compliant systems have potential to integrate. well within the constraints of laparoscopic procedures and telerobotic surgery. A load-path representation is used within a genetic algorithm to solve two gripper example problems. In addition, the paper illustrates the design and construction of an organ (kidney) manipulator for use in minimally invasive procedures.

Simulations of Mars Rover Traverses

Artemis (Adams-based Rover Terramechanics and Mobility Interaction Simulator) is a software tool developed to simulate rigid-wheel planetary rover traverses across natural terrain surfaces. It is based on mechanically realistic rover models and the use of classical terramechanics expressions to model spatially variable wheel-soil and wheel-bedrock properties. Artemiss capabilities and limitations for the Mars Exploration Rovers (Spirit and Opportunity) were explored using single-wheel laboratory-based tests, rover field tests at the Jet Propulsion Laboratory Mars Yard, and tests on bedrock and dune sand surfaces in the Mojave Desert. Artemis was then used to provide physical insight into the high soil sinkage and slippage encountered by Opportunity while crossing an aeolian ripple on the Meridiani plains and high motor currents encountered while driving on a tilted bedrock surface at Cape York on the rim of Endeavour Crater. Artemis will continue to evolve and is intended to be used on a continuing basis as a tool to help evaluate mobility issues over candidate Opportunity and the Mars Science Laboratory Curiosity rover drive paths, in addition to retrieval of terrain properties by the iterative registration of model and actual drive results.

Synthesis of Adaptive and Controllable Compliant Systems With Embedded Actuators and Sensors

This paper presents a framework for the design of a compliant system; that is, the concurrent design of a compliant mechanism with embedded actuators and embedded sensors. We focus on methods that simultaneously synthesize optimal structural topology and placement of actuators and sensors for maximum energy efficiency and adaptive performance, while satisfying various weight and performance constraints. The goal of this research is to lay a scientific foundation and a mathematical framework for distributed actuation and sensing within a compliant active structure. Key features of the methodology include (1) the simultaneous optimization of the location, orientation, and size of actuators concurrent with the compliant transmission topology and (2) the concepts of controllability and observability that arise from the consideration of control, and their implementation in compliant systems design. The methods used include genetic algorithms, graph searches for connectivity, and multiple load cases implemented with linear finite element analysis. Actuators, modeled as both force generators and structural compliant elements, are included as topology variables in the optimization. Results are provided for several studies, including: (1) concurrent actuator placement and topology design for a compliant amplifier and (2) a shape-morphing aircraft wing demonstration with three controlled output nodes. Central to this method is the concept of structural orthogonality, which refers to the unique system response for each actuator it contains. Finally, the results from the controllability problem are used to motivate and describe the analogous extension to observability for sensing.Copyright

Biomimetic compliant system for smart actuator-driven aquatic propulsion: Preliminary results

Biomimetic design takes principles from nature to employ in engineering problems. Such designs are hoped to be quiet, efficient, robust, and versatile, having taken advantage of optimization via natural selection. However, the emulation of specific biological devices poses a great challenge because of complicated, arbitrary, and over-redundant designs. Compliant mechanisms are of immediate appeal in addressing the problem of complex, biomimetic deformation because of their inherent flexibility and distributed compliance. The goal of this research is to develop a biologically-inspired hydrofoil for aquatic propulsion, by assembling planar compliant mechanism building blocks to generate complex 3-D deformations. The building block is a rib structure generated from topology optimization. An ADAMS model is then created to quickly visualize motion and estimate system characteristics. System refinement is achieved through further size and shape optimization of individual ribs. Testing of a single-rib and dual-actuator system is currently in progress. The preliminary results have demonstrated the potential of this combined approach to quickly identify and evaluate new applications that may result from building blocks.Copyright

Dynamic Modeling and Soil Mechanics for Path Planning of the Mars Exploration Rovers

To help minimize risk of high sinkage and slippage during drives and to better understand soil properties and rover terramechanics from drive data, a multidisciplinary team was formed under the Mars Exploration Rover (MER) project to develop and utilize dynamic computer-based models for rover drives over realistic terrains. The resulting tool, named ARTEMIS (Adams-based Rover Terramechanics and Mobility Interaction Simulator), consists of the dynamic model, a library of terramechanics subroutines, and the high-resolution digital elevation maps of the Mars surface. A 200-element model of the rovers was developed and validated for drop tests before launch, using MSC-Adams dynamic modeling software. Newly modeled terrain-rover interactions include the rut-formation effect of deformable soils, using the classical Bekker-Wong implementation of compaction resistances and bull-dozing effects. The paper presents the details and implementation of the model with two case studies based on actual MER telemetry data. In its final form, ARTEMIS will be used in a predictive manner to assess terrain navigability and will become part of the overall effort in path planning and navigation for both Martian and lunar rovers.Copyright

Design of Adaptive and Controllable Compliant Systems With Embedded Actuators and Sensors

We present a framework for the design of a compliant system, i.e., the concurrent design of a compliant mechanism with embedded actuators and sensors. Our methods simultaneously synthesize optimal structural topology and component placement for maximum energy efficiency and adaptive performance, while satisfying various weight and performance constraints. The goal of this research is to lay an algorithmic framework for distributed actuation and sensing within a compliant active structure. Key features of the methodology include (1) the simultaneous optimization of the location, orientation, and size of actuators (and sensors) concurrent with the compliant transmission topology, and (2) the implementation of controllability and observability concepts (both arising from consideration of control) in compliant systems design. The methods used include genetic algorithms, graph searches for connectivity, and multiple load cases implemented with linear finite element analysis. Actuators, modeled as both force generators and structural compliant elements, are included as topology variables in the optimization. The results from the controllability problem are used to motivate and describe the analogous extension to observability for sensing. Results are provided for several studies, including (1) concurrent actuator placement and topology design for a compliant amplifier, (2) a shape-morphing aircraft wing demonstration with three controlled output nodes, and (3) a load-distribution sensing wing structure with internal sensors. Central to this method is the concept of structure/component orthogonality, which refers to the unique system response for each component (actuator or sensor) it contains.

Automated Characterization and Compensation for a Compliant Mechanism Haptic Device

Compliant mechanisms and voice coil motors can be used in haptic device designs to eliminate bearings and achieve smooth friction-free motion. The accompanying return-to-center behavior can be compensated using feedforward control if a suitable multidimensional stiffness model is available. In this paper we introduce a method for automatic self-characterization and compensation, and apply it to a planar haptic interface that features a five-bar compliant mechanism. We show how actuators and position sensors already native to typical impedance-type haptic devices can readily accommodate stiffness compensation. Although a portion of the motor torque is consumed in compensation, the device achieves smooth friction-free articulation with simple, low tolerance, and economic components. Empirical models built on self-characterization data are compared to standard empirical and analytical models. We produce a model by self-characterization that requires no inversion and is directly useable for compensation. Although our prototype compliant mechanism, which we fabricated in plastic using fused deposition modeling, exhibited hysteresis (which we did not compensate), the return-to-center behavior was reliably reduced by over 95% with feedforward compensation based on the self-characterized model.

Bistable Mechanisms for Space Applications

Compliant bistable mechanisms are monolithic devices with two stable equilibrium positions separated by an unstable equilibrium position. They show promise in space applications as nonexplosive release mechanisms in deployment systems, thereby eliminating friction and improving the reliability and precision of those mechanical devices. This paper presents both analytical and numerical models that are used to predict bistable behavior and can be used to create bistable mechanisms in materials not previously feasible for compliant mechanisms. Materials compatible with space applications are evaluated for use as bistable mechanisms and prototypes are fabricated in three different materials. Pin-puller and cutter release mechanisms are proposed as potential space applications.