# Review of Recent Type-2 Fuzzy Controller Applications
## 3 Review of IT2 FLSs
### Industrial System Controllers  
IT2 FLCs have also been used in industrial operations, as well, e.g., inside a hot strip mill [63]. During the operation of the mill, a steel slab is heated, machined and rolled to a hot rolled coil. Typically, these operations will span more than 500 m, which will affect the temperature of the slab. It is very important to regulate the temperature, as the properties of steel will fluctuate. A T1 and IT2 FLC were implemented to control the coiler entry temperature. This was done by adjusting the cooling water flow to achieve the target entry temperature. In the experiments, the IT2 FLC achieved better performance and stability compared to the T1 FLC. It was concluded that the IT2 FLC controller is feasible in this design. Finishing strip mills also require the control of the rolling gap positions in order to achieve the desired strip head thickness. To do this, an X-ray gauge sensor was linked to an IT2 FLC [64]. Additional inputs are the transfer bar thickness, the entry width, the entry temperature, the target thickness, the output width, the output temperature, the standing work roll diameter, the work roll speed, the stand entry thickness, the stand exit thickness, the stand rolling force and the percent carbon of the strip. The finishing mill stand screw was adjusted to target the required thickness. Thefeasibility of the proposed IT2 FLC was also shown, and it was found that this controller equalized the performance of the finishing mill stand screw and achieved the target strip thickness while under high uncertainty. Precise positioning is required for the fabrication of nano- and micro-components in the semiconductor industry. Since these components are very small, an IT2 FLC was proposed for a linear ultrasonic motor [65]. The simulation results show that the adaptive IT2 did not require prior knowledge of the plant. It was concluded that the IT2 FLC was more effective and robust over the T1 FLC. IT2 FLCs have been used in AC motors, such as permanent magnet synchronous motors (PMSM) [66] or permanent magnet linear synchronous motor (PMLSM) [67]. PMSM are used in many applications requiring high efficiency and high torque-to-weight ratios. Since they are AC systems, their controllers are typically designed from a PID or PI regulator. These are very efficient; however, they are also subjected to uncertainties, such as varying loads, plant parameter variations and other non-linarites. An IT2 FLC was designed to account for these uncertainties. It was tested in different ways with either extreme parameter variations or external disturbances. It was found that the IT2 FLC was able to maintain the tracking errors within an acceptable interval. PMSMs offer many benefits; however, uncertainties in the drive mechanism can affect their performance, since there are no ball screws or gears. External loads, non-linear friction forces and parameter variations are some examples. In order to account for these, IT2 FLC have been designed and used. First, the self-adaptive IT2 FLC was run in order to learn the inverse kinematics of the system. Then, the inverse self-adaptive IT2 FLC is built with error feedback. From the experimental results, it was shown that the IT2 FLC outperformed the T1 FLC. An induction motor was also controlled using a T2 FLC [68]. This motor used space vector pulse width modulation (PWM) to control the torque of the motor. Typically, these are run with a proportional-integral (PI) controller; however, a PI controller does not provide efficient performance during sudden changes in the load or speed. It was shown that the IT2 FLC performed better than the PI controller. The flux distortion, starting current, torque pulsation and speed regulation were much lower with the IT2 FLC. This was then tested using a prototype DSPACE DS1104. It was found that the typical PI controller had a current total harmonic distortion of 3.3%, while the T2 FLC reduced that to 2.3%.