Researchers at the University of Edinburgh in the UK have built a prototype “hairy robotic gripper” that is inspired by the hairs found on ant jaws.

Ants are not only excellent nest builders but are also expert foragers, able to carry food and other items that can be many times their own weight.

Part of that ability lies in their powerful jaws, with snap-jaw ants able to close their mandibles at a top speed of 400 kmph.

Ant jaws also feature small hairs that are used to sense items but also to mechanically stabilise their grip on the objects.

Edinburgh researchers filmed ants and the sequence of movements they do when picking up seeds and other things. They then used this to build a robot gripper.

The device consists of two aluminium plates that each contain four rows of “hairs” made from thermoplastic polyurethane.

The hairs are 20 mm long and 1 mm in diameter, protruding in a v-shape. This allowing the hairs to surround circular objects, which can be particularly difficult to grasp and hold onto using paraellel plates.

In tests picking up 30 different household items including a jam jar and shampoo bottle (see video), adding hairs to the gripper increased the prototype’s grasp success rate from 64% to 90%.

The researchers think that such a device could be used in environmental clean-up as well as in construction and agriculture.

Barbara Webb from the University of Edinburgh, who led the research, says the work is “just the first step”.

“Now we can see how [ants’] antennae, front legs and jaws combine to sense, manipulate, grasp and move objects – for instance, we’ve discovered how much ants rely on their front legs to get objects in position,” she adds. “This will inform further development of our technology.”

The post Ants’ hairy jaws help robots to get a grip appeared first on Physics World.

When a mantis shrimp uses shock waves to strike and kill its prey, how does it prevent those shock waves from damaging its own tissues? Researchers at Northwestern University in the US have answered this question by identifying a structure within the shrimp that filters out harmful frequencies. Their findings, which they obtained by using ultrasonic techniques to investigate surface and bulk wave propagation in the shrimp’s dactyl club, could lead to novel advanced protective materials for military and civilian applications.

Dactyl clubs are hammer-like structures located on each side of a mantis shrimp’s body. They store energy in elastic structures similar to springs that are latched in place by tendons. When the shrimp contracts its muscles, the latch releases, releasing the stored energy and propelling the club forward with a peak force of up to 1500 N.

This huge force (relative to the animal’s size) creates stress waves in both the shrimp’s target – typically a hard-shelled animal such as a crab or mollusc – and the dactyl club itself, explains biomechanical engineer Horacio Dante Espinosa, who led the Northwestern research effort. The club’s punch also creates bubbles that rapidly collapse to produce shockwaves in the megahertz range. “The collapse of these bubbles (a process known as cavitation collapse), which takes place in just nanoseconds, releases intense bursts of energy that travel through the target and shrimp’s club,” he explains. “This secondary shockwave effect makes the shrimp’s strike even more devastating.”

Protective phononic armour

So how do the shrimp’s own soft tissues escape damage? To answer this question, Espinosa and colleagues studied the animal’s armour using transient grating spectroscopy (TGS) and asynchronous optical sampling (ASOPS). These ultrasonic techniques respectively analyse how stress waves propagate through a material and characterize the material’s microstructure. In this work, Espinosa and colleagues used them to provide high-resolution, frequency-dependent wave propagation characteristics that previous studies had not investigated experimentally.

The team identified three distinct regions in the shrimp’s dactyl club. The outermost layer consists of a hard hydroxyapatite coating approximately 70 μm thick, which is durable and resists damage. Beneath this, an approximately 500 μm-thick layer of mineralized chitin fibres arranged in a herringbone pattern enhances the club’s fracture resistance. Deeper still, Espinosa explains, is a region that features twisted fibre bundles organized in a corkscrew-like arrangement known as a Bouligand structure. Within this structure, each successive layer is rotated relative to its neighbours, giving it a unique and crucial role in controlling how stress waves propagate through the shrimp.

“Our key finding was the existence of phononic bandgaps (through which waves within a specific frequency range cannot travel) in the Bouligand structure,” Espinosa explains. “These bandgaps filter out harmful stress waves so that they do not propagate back into the shrimp’s club and body. They thus preserve the club’s integrity and protect soft tissue in the animal’s appendage.”

 The team also employed finite element simulations incorporating so-called Bloch-Floquet analyses and graded mechanical properties to understand the phonon bandgap effects. The most surprising result, Espinosa tells Physics World, was the formation of a flat branch around the 450 to 480 MHz range, which correlates to frequencies arising from bubble collapse originating during club impact.

Evolution and its applications

For Espinosa and his colleagues, a key goal of their research is to understand how evolution leads to natural composite materials with unique photonic, mechanical and thermal properties. In particular, they seek to uncover how hierarchical structures in natural materials and the chemistry of their constituents produce emergent mechanical properties. “The mantis shrimp’s dactyl club is an example of how evolution leads to materials capable of resisting extreme conditions,” Espinosa says. “In this case, it is the violent impacts the animal uses for predation or protection.”

The properties of the natural “phononic shield” unearthed in this work might inspire advanced protective materials for both military and civilian applications, he says. Examples could include the design of helmets, personnel armour, and packaging for electronics and other sensitive devices.

In this study, which is described in Science, the researchers analysed two-dimensional simulations of wave behaviour. Future research, they say, should focus on more complex three-dimensional simulations to fully capture how the club’s structure interacts with shock waves. “Designing aquatic experiments with state-of-the-art instrumentation would also allow us to investigate how phononic properties function in submerged underwater conditions,” says Espinosa.

The team would also like to use biomimetics to make synthetic metamaterials based on the insights gleaned from this work.

The post ‘Phononic shield’ protects mantis shrimp from its own shock waves appeared first on Physics World.

Globular springtails (Dicyrtomina minuta) are small bugs about five millimetres long that can be seen crawling through leaf litter and garden soil. While they do not have wings and cannot fly, they more than make up for it with their ability to hop relatively large heights and distances.

This jumping feat is thanks to a tail-like appendage on their abdomen called a furcula, which is folded in beneath their body, held under tension.

When released, it snaps against the ground in as little as 20 milliseconds, flipping the springtail up to 6 cm into the air and 10 cm horizontally.

Researchers at the Harvard John A Paulson School of Engineering and Applied Sciences have now created a robot that mimics this jumping ability.

They modified a cockroach-inspired robot to include a latch-mediated spring actuator, in which potential energy is stored in an elastic element – essentially a robotic fork-like furcula.

Via computer simulations and experiments to control the length of the linkages in the furcula as well as the energy stored in them, the team found that the robot could jump some 1.4 m horizontally, or 23 times its body length – the longest of any existing robot relative to body length.

The work could help design robots that can traverse places that are hazardous to humans.

“Walking provides a precise and efficient locomotion mode but is limited in terms of obstacle traversal,” notes Harvard’s Robert Wood. “Jumping can get over obstacles but is less controlled. The combination of the two modes can be effective for navigating natural and unstructured environments.”

The post Harvard’s springtail-like jumping robot leaps into action appeared first on Physics World.