# A State-of-the-Art Review on Robots and Medical Devices Using Smart Fluids and Shape Memory Alloys
## 3 Robots Using SMA
### SMA-Based Robots
In particular, a complex thermal-electrical-mechanical model is required to correctly represent the behavior of the SMA described in Section 3.1. However, this is challenging because of its strong temperature dependence. The property changes will cause a significant backlash-like hysteresis loop in a highly nonlinear manner in open-loop control responses, which results in response delays and steady-state errors, and limit-cycle issues in the position control \begin{table}
\begin{tabular}{c c c} \hline \hline
**Robots** & **Biomimetic** & **References** \\ \hline Micro-fish & Fish fin & [53; 54; 55] \\ Crawling & _C. elegans_ & [56] \\ Tentacle & Starfish & [57; 58] \\ Buoyance & Jellyfish & [59; 60] \\ Swimming & Turtle & [61; 62] \\ Linear & Inchworm & [63; 64] \\ Flytrap & Venus flytrap & [65] \\ Jumping & Froghopper & [66] \\ Flying & Bat, Dragonfly & [67; 68] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of state-of-the-art bio-inspired robotic applications using SMA actuators. of SMA actuators with a conventional feedback controller, such as a PID controller [70]. The robust position control of SMA actuators for compensating hysteresis is therefore one of the interesting research areas in the smart-material community. For example, the sliding mode control (SMC) was applied to control the arm positions of a flexible robot [71; 72]. Advanced SMC schemes, such as an adaptive sliding-mode control with a PID tuning method [73], and an intelligent sliding mode control [74], are proposed to achieve robustness against the SMA hysteresis phenomenon. [PERSON] et al. [75] experimentally demonstrated that a simple time delay control (SDC), without a precise actuator model, can be effective for actuating an SMA wire actuator. The open-loop pulse width modulation (PWM) control was also developed to reduce the SMA actuator energy consumption [76]. This control method with a metal-oxide-semiconductor field-effect transistor (MOSFET) switching circuit, can also be used for safely powering the SMA wire actuators across a wide range of speeds or input voltages, which will in turn ensure a better durability, by preventing overheating of the SMA wires [77]. Numerous new approaches for the design and control of SMA actuators have been explored. For example, [PERSON] et al. [78] proposed a segmented SMA wire actuator, which is divided into many segments, and their thermal states are controlled individually as a group of finite-state machines. Then, instead of driving a current to the entire SMA wire and controlling the wire length based on the analog strain-temperature characteristics, this approach controls the binary state (hot or cold) of individual segments, which improves efficiency. The SMA wire itself can be the sensing element for the control of the SMA actuator. The classic example of this is to take advantage of the electrical resistance feedback, which eliminates the need for a position sensor, in this case by utilizing the SMA's electrical resistance feedback. The position control system for the SMA wire actuator with electrical-resistance feedback was proposed by [PERSON] et al. [79], and has been recently advanced by [PERSON] et al. [80]. We use the embedded SMA wire in composites, both as an actuator and as a strain sensor. [PERSON] et al. [81] proposed using the SMA wire as a strain sensor to obtain an actuation trigger signal, based on the variation of the SMA electric resistance correlated with the strain.