A shape memory alloy–actuated soft crawling robot based on adaptive differential friction and enhanced antagonistic configuration

This article presents a soft crawling robot prototype with a simple architecture inspired by inchworms. The robot functionally integrates the torso (body) and feet in a monolithic curved structure that only needs a single shape memory alloy coil and differential friction to actuate it. A novel foot configuration is proposed, which makes the two feet, with an anti-symmetrical friction layout, can be alternately anchored, to match the contraction–recovery sequence of the body adaptively. Based on the antagonistic configuration between the shape memory alloy actuator and the elastic body, a vertically auxiliary spring was adopted to enhance the interaction mechanism. Force and kinematic analysis was undertaken, focusing on the parametric design of the special foot configuration. A miniature robot prototype was then 3D-printed (54 mm in length and 9.77 g in weight), using tailored thermoplastic polyurethane elastomer as the body material. A series of experimental tests and evaluations were carried out to assess its performance under different conditions. The results demonstrated that under appropriate actuation conditions, the compact robot prototype could accomplish a relative speed of 0.024 BL/s (with a stride length equivalent to 27% of its body length) and bear a load over five times to its own weight.

Motion of a Legged Bidirectional Miniature Piezoelectric Robot Based on Traveling Wave Generation

This article reports on the locomotion performance of a miniature robot that features 3D-printed rigid legs driven by linear traveling waves (TWs). The robot structure was a millimeter-sized rectangular glass plate with two piezoelectric patches attached, which allowed for traveling wave generation at a frequency between the resonant frequencies of two contiguous flexural modes. As a first goal, the location and size of the piezoelectric patches were calculated to maximize the structural displacement while preserving a standing wave ratio close to 1 (cancellation of wave reflections from the boundaries). The design guidelines were supported by an analytical 1D model of the structure and could be related to the second derivative of the modal shapes without the need to rely on more complex numerical simulations. Additionally, legs were bonded to the glass plate to facilitate the locomotion of the structure; these were fabricated using 3D stereolithography printing, with a range of lengths from 0.5 mm to 1.5 mm. The optimal location of the legs was deduced from the profile of the traveling wave envelope. As a result of integrating both the optimal patch length and the legs, the speed of the robot reached as high as 100 mm/s, equivalent to 5 body lengths per second (BL/s), at a voltage of 65 Vpp and a frequency of 168 kHz. The blocking force was also measured and results showed the expected increase with the mass loading. Furthermore, the robot could carry a load that was 40 times its weight, opening the potential for an autonomous version with power and circuits on board for communication, control, sensing, or other applications.

Developing an adaptable pipe inspection robot using shape memory alloy actuators

To detect and repair the faults existing in pipes and narrow ducts in the industry, access to the inside of these pipes is often required. In this article, the conceptual design for a miniature robot for inspecting the inner walls of pipes is presented, such that the proposed robot can operate adaptably and freely in vertical, inclined, and bent paths. The robot utilizes a simple mechanism based on shape memory alloy actuators for adjusting the contact force between the robot and the inner wall of the pipe. Use of shape memory alloys as actuators for the adaptive part will result in a smaller and lighter robot, further increasing its mobility in narrower ducts. Modeling, simulation, and control of the proposed system is conducted and simulation results are validated by performing practical laboratory experiments on a built prototype.

A Highly Manoeuvrable and Untethered Under-Actuated Legged Piezoelectric Miniature Robot

This paper presents the design of a highly manoeuvrable and untethered under-actuated legged piezoelectric miniature robot called PISCES. It comprises of a piezoelectric patch bonded onto a thin diamond-shaped aluminium plate to form a planar unimorph piezoelectric actuator, with three rigidly attached legs to generate locomotion. Unlike other under-actuated robots found in literature which uses compliant mechanisms, our robot utilizes three different standing wave vibration modes of a thin diamond-shaped aluminium plate and well positioned rigid leg positions to achieve forward, clockwise rotation and anticlockwise rotation motion using a single piezoelectric patch. This approach have the benefit of generating a more predefined motion and thus more controllable. A finite element analysis approach is proposed to understand the modal vibration of the 2D unimorph actuator and how the geometric placement of the rigid legs together with the robot center of mass can be utilized to achieve under-actuated planar locomotion is described in detail. To verify the proposed locomotion, PISCES of a size of 90 × 60 × 11 mm, weight of 21 g is built. It is able to achieve a linear speed of 203.5 mm/s for forward motion, an angular speeds of 7.7 Revolution Per Minute (RPM) for clockwise rotation and an angular speed of 10.6 RPM for anticlockwise rotation using an input sinusoidal voltage of 100 V amplitude. Under a payload of 100 g, it moves with a linear speed of 110.8 mm/s and angular speeds of 4.1 RPM clockwise and 12.5 RPM anticlockwise. A tether-less remotely driven PISCES featuring a full suite of onboard electronics, and a more detailed experimental verification, analysis and characterization of PISCES are also demonstrated in this paper.

The Drone and the Honey Bee

While scientists rush to pin down the cause of colony collapse disorder and race to find a cure, engineers have wondered whether we might one day supplement real bees with mechanical ones. Called DelFly, a miniature robot has been built by an engineering team of the Micro Air Vehicles Laboratory at Delft University of Technology in the Netherlands. The engineers there have various practical applications in mind. For example, when perfected, the bots could flit around greenhouses spotting diseases with their cameras. The robots could also be fitted with apparatuses to perform an even more vital and insect-like task—pollinating crops.