Daniel M. Aukes

Self-folding origami: shape memory composites activated by uniform heating

Self-folding is an approach used frequently in nature for the efficient fabrication of structures, but is seldom used in engineered systems. Here, self-folding origami are presented, which consist of shape memory composites that are activated with uniform heating in an oven. These composites are rapidly fabricated using inexpensive materials and tools. The folding mechanism based on the in-plane contraction of a sheet of shape memory polymer is modeled, and parameters for the design of composites that self-fold into target shapes are characterized. Four self-folding shapes are demonstrated: a cube, an icosahedron, a flower, and a Miura pattern; each of which is activated in an oven in less than 4 min. Self-sealing is also investigated using hot melt adhesive, and the resulting structures are found to bear up to twice the load of unsealed structures.

Design and testing of a selectively compliant underactuated hand

Motivated by the requirements of mobile manipulation, a compliant underactuated hand, capable of locking individual joints, has been developed. Locking is accomplished with electrostatic brakes in the joints and significantly increases the maximum pullout forces for power grasps. In addition, by locking and unlocking joints, the hand can adopt configurations and grasp sequences that would otherwise require a fully actuated solution. Other features of the hand include an integrated sensing suite that uses a common transduction technology on flexible printed circuits for tactile and proprioceptive sensing. The hand is analyzed using a three-dimensional rigid body analysis package with efficient simulation of compliant mechanisms and contacts with friction. This package allows one to evaluate design tradeoffs among link lengths, required tendon tensions, spring stiffnesses and braking requirements to grasp and hold a wide range of objects. Results of grasping and pullout tests confirm the utility of the simulations.

Selectively compliant underactuated hand for mobile manipulation

The demands of mobile manipulation are leading to a new class of multi-fingered hands with a premium on being lightweight and robust as well as being able to grasp and perform basic manipulations with a wide range of objects. A promising approach to addressing these goals is to use compliant, underactuated hands with selectively lockable degrees of freedom. This paper presents the design of one such hand that combines series-elastic actuation and electrostatic braking at the joints. A numerical analysis shows how the maximum pullout force varies as a function of kinematic parameters, spring forces at the joints and brake torques.

An end-to-end approach to making self-folded 3D surface shapes by uniform heating.

This paper presents an end-to-end approach for creating 3D shapes by self-folding planar sheets activated by uniform heating. These shapes can be used as the mechanical bodies of robots. The input to this process is a 3D geometry (e.g. an OBJ file). The output is a physical object with the specified geometry. We describe an algorithm pipeline that (1) identifies the overall geometry of the input, (2) computes a crease pattern that causes the sheet to self-fold into the desired 3D geometry when activated by uniform heating, (3) automatically generates the design of a 2D sheet with the desired pattern and (4) automatically generates the design files required to fabricate the 2D structure. We demonstrate these algorithms by applying them to complex 3D shapes. We demonstrate the fabrication of a self-folding object with over 50 faces from automatically generated design files.

Varying spring preloads to select grasp strategies in an adaptive hand

We describe an underactuated hand mechanism that is able to adopt a wide range of grasp types by varying the internal forces in its fingers. The adjustment is accomplished by varying the preloads of springs, which affect the grasp stability and stiffness for large and small objects. Preload adjustment can be accomplished with low power, non-backdrivable actuators in the fingers. The analysis is presented first for a planar, two-fingered hand to illustrate the trends and tradeoffs associated with variations in preload. The results are then applied numerically to a three fingered hand with three phalanges per finger. This design is a prototype for a hand to be used in an underwater oil drilling platform under conditions of low friction and uncertain object locations.

Self-folding with shape memory composites at the millimeter scale

Self-folding is an effective method for creating 3D shapes from flat sheets. In particular, shape memory composites—laminates containing shape memory polymers—have been used to self-fold complex structures and machines. To date, however, these composites have been limited to feature sizes larger than one centimeter. We present a new shape memory composite capable of folding millimeter-scale features. This technique can be activated by a global heat source for simultaneous folding, or by resistive heaters for sequential folding. It is capable of feature sizes ranging from 0.5 to 40 mm, and is compatible with multiple laminate compositions. We demonstrate the ability to produce complex structures and mechanisms by building two self-folding pieces: a model ship and a model bumblebee.

An analytic framework for developing inherently-manufacturable pop-up laminate devices

Spurred by advances in manufacturing technologies developed around layered manufacturing technologies such as PC-MEMS, SCM, and printable robotics, we propose a new analytic framework for capturing the geometry of folded composite laminate devices and the mechanical processes used to manufacture them. These processes can be represented by combining a small set of geometric operations which are general enough to encompass many different manufacturing paradigms. Furthermore, such a formulation permits one to construct a variety of geometric tools which can be used to analyze common manufacturability concepts, such as tool access, part removability, and device support. In order to increase the speed of development, reduce the occurrence of manufacturing problems inherent with current design methods, and reduce the level of expertise required to develop new devices, the framework has been implemented in a new design tool called popupCAD, which is suited for the design and development of complex folded laminate devices. We conclude with a demonstration of utility of the tools by creating a folded leg mechanism.

A compliant underactuated hand with suction flow for underwater mobile manipulation

Fingertip suction is investigated using a compliant, underactuated, tendon-driven hand designed for underwater mobile manipulation. Tendon routing and joint stiffnesses are designed to provide ease of closure while maintaining finger rigidity, allowing the hand to pinch small objects, as well as secure large objects, without diminishing strength. While the hand is designed to grasp a range of objects, the addition of light suction flow to the fingertips is especially effective for small, low-friction (slippery) objects. Numerical simulations confirm that changing suction parameters can increase the object acquisition region, providing guidelines for future versions of the hand.

Model driven design for flexure-based Microrobots

This paper presents a non-linear, dynamic model of the flexure-based transmission in the Harvard Ambulatory Microrobot (HAMR). The model is derived from first principles and has led to a more comprehensive understanding of the components in this transmission. In particular, an empirical model of the dynamic properties of the compliant Kapton flexures is developed and verified against theoretical results from beam and vibration theory. Furthermore, the fabrication of the piezoelectric bending actuators that drive the transmission is improved to match theoretical performance predictions. The transmission model is validated against experimental data taken on HAMR for the quasi-static (1-10 Hz) operating mode, and is used to redesign the transmission for improved performance in this regime. The model based redesign results in a 266% increase in the work done by the foot when compared to a previous version of HAMR. This leads to a payload capacity of 2.9g, which is ~ 2× the robots mass and a 114% increase. Finally, the model is validated in the dynamic regime (40-150 Hz) and the merits of a second order linear approximation are discussed.

The flying monkey: A mesoscale robot that can run, fly, and grasp

The agility and ease of control make a quadrotor aircraft an attractive platform for studying swarm behavior, modeling, and control. The energetics of sustained flight for small aircraft, however, limit typical applications to only a few minutes. Adding payloads - and the mechanisms used to manipulate them - reduces this flight time even further. In this paper we present the flying monkey, a novel robot platform having three main capabilities: walking, grasping, and flight. This new robotic platform merges one of the worlds smallest quadrotor aircraft with a lightweight, single-degree-of-freedom walking mechanism and an SMA-actuated gripper to enable all three functions in a 30 g package. The main goal and key contribution of this paper is to design and prototype the flying monkey that has increased mission life and capabilities through the combination of the functionalities of legged and aerial robots.