Twisted and coiled polymer (TCP) can generate large stroke and output high power density, making it a promising artificial muscle. Thermally induced muscles fabricated from nylon or other polymer fibers can be used in robotic, biomedical devices, and energy-harvesting equipment. While fibers with different shapes and materials have different optimal process parameters. Understanding mechanisms of TCP forming and the impact of process parameters is critical to explore stronger, more powerful artificial muscles. In this paper, an elastic-rod-theory-based model was established for capturing the quantitative relationship between tensile actuation and fabrication load. Further experimental results agree with model calculation and TCP muscles used in our research reaches maximum stroke of 52.6%, strain up to 9.8 MPa, and power density of 211.89 J/kg.

Twisted and coiled polymer (TCP) actuators are becoming increasingly prevalent in soft robotic fields due to their powerful and hysteresis-free stroke, large specific work density, and ease of fabrication. This paper presents a soft crawling robot with spike-inspired robot feet which can deform and crawl like an inchworm. The robot mainly consists of two leaf springs, connection part, robot feet, and two TCP actuators. A system level model of a soft crawling robot is presented for flexible and effective locomotion. Such a model can offer high-efficiency design and flexible locomotion of the crawling robot. Results show that the soft crawling robot can move at a speed of 0.275 mm/s when TCP is powered at 24 V.

Purpose Selective laser melting (SLM) enables the fabrication of lightweight and complex metallic structures. Support structures are required in the SLM process to successfully produce parts. Supports are typically lattice structures, which cost much time and material to manufacture. Besides, the manufacturability of these supports is undesirable, which may impact the quality of parts or even fail the process. The purpose of this paper is to investigate the efficiency and mechanical properties of advanced internal branch support structures for SLM. Design/methodology/approach The theoretic weight of a branch support and a lattice support of the same plane were calculated and compared. A group of standard candidates of branch support structures were manufactured by SLM. The weight and scanning time of specimens with different design parameters were compared. Then, these samples were tested using an MTS Insight 30 compression testing machine to study the influence of different support parameters on mechanical strength of the support structures. Findings The results show that branch type supports can save material, energy and time used needed for their construction. The yield strength of the branch increases with the branch diameter and inclined branch angle in general. Furthermore, branch supports have a higher strength than traditional lattice supports. Originality/value To the best of the authors’ knowledge, this is the first work investigating production efficiency and mechanical properties of branch support structures for SLM. The findings in this work are valuable for development of advanced optimal designs of efficient support structures for SLM process.

Twisted and coiled polymer (TCP) actuator has many advantages such as high contraction capability, high work density, low cost materials, and easiness of fabrication, making it promising for applications in biomedical devices, soft robotic, and energy-harvesting equipment. However, convenient and effective control of TCP actuators still remain some challenges. In this paper, we use an accurate straintemperature and force-temperature model of TCP actuators to design a simple and efficient closed-loop PID control system. The validity of the proposed controllers is investigated through numerical simulations and experiments. The results show good control performance with minimum tracking errors which is less than 3% in our work. Such accuracy is ideal for many engineering fields and robotic designs.

Abstract:The purpose of this paper is to present a new design method of lightweight parts fabricated by selective laser melting (SLM) based on the "Skin-Frame" and to explore the influence of fabrication defects on SLM parts with different sizes. Some standard lattice parts were designed according to the Chinese GB/T 1452-2005 standard and manufactured by SLM. Then these samples were tested in an MTS Insight 30 compression testing machine to study the trends of the yield process with different structure sizes. A set of standard cylinder samples were also designed according to the Chinese GB/T 228-2010 standard. These samples, which were made of iron-nickel alloy (IN718), were also processed by SLM, and then tested in the universal material testing machine INSTRON 1346 to obtain their tensile strength. Furthermore, a lightweight redesigned method was researched. Then some common parts such as a stopper and connecting plate were redesigned using this method. These redesigned parts were fabricated and some application tests have already been performed. The compression testing results show that when the minimum structure size is larger than 1.5 mm, the mechanical characteristics will hardly be affected by process defects. The cylinder parts were fractured by the universal material testing machine at about 1069.6 MPa. These redesigned parts worked well in application tests, with both the weight and fabrication time of these parts reduced more than 20%.