# A State-of-the-Art Review on Robots and Medical Devices Using Smart Fluids and Shape Memory Alloys
## 2 Robots Using ERF and MRF
### MRF-Based Robots  
MRFs have been for the first time applied to vehicle shock absorbers, and some of the passenger vehicles integrated with MR dampers are currently available on the market [8; 9]. The application of MRFs to robotics has been actively researched since 2000. Initially, the feasibility of MRFs as robotic actuators was both conceptually and experimentally studied [10]. There are two possible approaches when investigating the actuating characteristics of MRFs. One is to make valve systems and produce an active control force in closed-loop systems. The other is to directly use MRFs as actuators, by generating a flow motion in three different flow modes (flow, shear, and squeeze), in which a semi-active damping force is normally produced in open- or closed-loop control systems. Recently, [PERSON] and [PERSON] [11] proposed a new adaptive control method to compensate for the inherent hysteretic phenomenon of MRFs, and to develop high-performance robot actuators. In order to validate the proposed control scheme, a small-sized two degrees-of-freedom (2-DOF) MR-actuator robot manipulator was manufactured, and the higher accuracy of its torque-control results, compared to the case without the hysteretic compensator, was presented with various frequency torque trajectories. The state-of-the-art robotic applications using MRF actuators are summarized in Table 2. A robot application device with MRFs, a deformable gripper that handled implements such as a writing pen, was invented in [12]. This gripper could be deformed in conformance with the user's hands and fingers, with the gripper comprising a tubular sleeve in which the MRF flowed radially. The deformability of the gripper was controlled by a sliding mechanism activated by an electromagnet. A robot gripper for handling delicate food products using MRFs was also developed in [13]. In this work, a two-finger gripper was manufactured. When the MRF, in pouches, reached the sides of the object, the pouches started to deform without stretching the pouch material. One of the gripper arms was fitted with a strain-gauge force sensor, which allowed for multiple gripping modes. The gripping force when handling various fruits and vegetables, such as carrots and strawberries, was measured through both open-loop setting speeds and closed-loop control methods, associated with a proportional-integral-derivative (PID) controller. It was concluded that the gripping force was evenly spread over a large surface, reducing the risk of bruising, and that the geometric dimensions of the gripper were crucial in achieving a universal gripper, able to handle any size or shape of food products. More recently, [PERSON] et al. [14] proposed a new type of 3D-haptic gripper for tele-manipulation, using an MR brake system. This haptic gripper transfers the rolling torque, grasping force, and approach force from the slave manipulator to the master operator. Figure 2 shows a schematic configuration of the 3D-haptic gripper which can be applied in surgical robots, where the gripper is attached to a stationary base, and the master manipulator and the haptic gripper are separated. The haptic gripper consists of two rotary MR brakes. These are the grasping and rolling MRBs, and two identical linear MRBs to reflect the approach force. The shaft of the rolling MRB is fixed to the body of the haptic gripper while its housing is attached to the stationary base. The shaft of the grasping MRB is connected to gear 2 while its housing is fixed to the gripper body. The gear 2 externally mates with gear 1. On gears 1 and 2, the two shafts of the linear MRBs are attached. The housings of the linear MRBs, on which the handles of the gripper are attached, can move relative to their shafts. By controlling the applied currents of the MRBs according to signals received from the slave sensors, the grasping force, rolling torque and approach force from the slave can be reflected to the human operator [14]. In this work, the principal design parameters, such as the magnetic pole, are determined