Person:

Yang, Dian

This paper describes several noncontact methods of orienting objects in 3D space using Magnetic Levitation (MagLev). The methods use two permanent magnets arranged coaxially with like poles facing and a container containing a paramagnetic liquid in which the objects are suspended. Absent external forcing, objects levitating in the device adopt predictable static orientations; the orientation depends on the shape and distribution of mass within the objects. The orientation of objects of uniform density in the MagLev device shows a sharp geometry-dependent transition: an analytical theory rationalizes this transition and predicts the orientation of objects in the MagLev device. Manipulation of the orientation of the levitating objects in space is achieved in two ways: (i) by rotating and/or translating the MagLev device while the objects are suspended in the paramagnetic solution between the magnets; (ii) by moving a small external magnet close to the levitating objects while keeping the device stationary. Unlike mechanical agitation or robotic selection, orienting using MagLev is possible for objects having a range of different physical characteristics (e.g., different shapes, sizes, and mechanical properties from hard polymers to gels and fluids). MagLev thus has the potential to be useful for sorting and positioning components in 3D space, orienting objects for assembly, constructing noncontact devices, and assembling objects composed of soft materials such as hydrogels, elastomers, and jammed granular media.

Soft robotics is a growing field where scientists and engineers collaborate to design machines that collaborate safely with humans (namely “collaborative robot”), and manipulate soft or delicate objects safely. Soft pneumatic actuators are excellent tools in building soft robots, since both the elastomer used in building the actuators and the air used to power them are naturally compliant. This compliance distributes the contact force over the area of contact, and limits the contact pressure. Soft pneumatic actuators changes shape with pressure, and use strain-limiting components imbedded in an elastomeric enclosure to generate various motions.

This dissertation explores design and fabrication of soft pneumatic actuators by combining vacuum with reversible buckling of elastomeric beams. Buckling is a classical mechanical instability often seen as a failure mode in hard materials. The reversible buckling of elastomeric beams, however, allows buckling to be harnessed as a method to generate a range of motion, and allows the fabrication of actuators that mimic the performance of actuators (i.e. muscles) found in nature.

Chapter 1 provides a short overview of the history of soft pneumatic actuators, and of the use of vacuum instead of pressure as a source of power. Chapter 2 and Appendix I describe rotary soft pneumatic actuators—the buckling actuator—based on vacuum and buckling of elastomeric beams. Chapter 3 and Appendix II describe the design of linear soft pneumatic actuators—vacuum-actuated muscle-inspired pneumatic structures (VAMPs)—based on the same technology, which mimics the mechanical performance and many useful features of human muscle. Chapter 4 and Appendix III describe a design of vacuum-actuated soft linear actuators (VASAs) that overcome the usual limit of one atmosphere in the output pressure by generating a mechanical advantage. Appendix IV demonstrates that the buckling of arrays of elastomeric beams can also be used in building soft metamaterials with useful functions, such as shape memory metamaterials. Beyond soft pneumatics actuators, novel methods of non-damaging manipulations, such as magnetic levitation, can prove useful in orientation and examination of objects (Appendix V, VI).

We show that the solid−solid friction between bulk chiral molecular solids can depend on the relative chirality of the two materials. In menthol and 1-phenyl-1-butanol, heterochiral friction is smaller than homochiral friction, while in ibuprofen, heterochiral friction is larger. Chiral asymmetries in the coefficient of sliding friction vary with temperature and can be as large as 30%. In the three compounds tested, the sign of the difference between heterochiral and homochiral friction correlated with the sign of the difference in melting point between racemate (compound or conglomerate) and pure enantiomer. Menthol and ibuprofen each form a stable racemic compound, while 1-phenyl-1-butanol forms a racemic conglomerate. Thus, a difference between heterochiral and homochiral friction does not require the formation of a stable interfacial racemic compound. Measurements of chirality-dependent friction provide a unique means to distinguish the role of short-range intermolecular forces from all other sources of dissipation in the friction of bulk molecular solids

This paper demonstrates a new soft structure that uses a meso- or macro-scale elastic instability to generate a shape-memory effect similar to that exhibited by a ferroelastic material. It demonstrates the phase transitions, state switching, and shape-memory effects in this system, both in experiment and in simulation. The new class of materials described in the paper is potentially useful, since it comprises what are effectively ‘‘shape-memory alloys’’ of arbitrarily low modulus and arbitrarily large remnant strain. The reproduction of properties of materials usually associated with atomic- or molecular-level changes in structure using meso-scale structural opens the door to development of new, soft materials with new properties and functions.

The mechanical features of biological muscles are difficult to reproduce completely in synthetic systems. A new class of soft pneumatic structures (vacuum-actuated muscle-inspired pneumatic structures) is described that combines actuation by negative pressure (vacuum), with cooperative buckling of beams fabricated in a slab of elastomer, to achieve motion and demonstrate many features that are similar to that of mammalian muscle.

Magnetic levitation (MagLev) enables rapid and non-destructive quality control of plastic parts. The feasibility of MagLev as a method to: i) rapidly assess injection-molded plastic parts for defects during process optimization, ii) monitor the degradation of plastics after exposure to harsh environmental conditions, and iii) detect counterfeit polymers by density is demonstrated.

Soft, pneumatic actuators that buckle when interior pressure is less than exterior provide a new mechanism of actuation. Upon application of negative pneumatic pressure, elastic beam elements in these actuators undergo reversible, cooperative collapse, and generate a rotational motion. These actuators are inexpensive to fabricate, lightweight, easy to control, and safe to operate. They can be used in devices that manipulate objects, locomote, or interact cooperatively with humans.