How does the Time Delay of an ER Fluid´s Response Affect Control Performance of Servo-systems?

We previously developed a particle type ER (electro-rheological) fluid damper in which viscosity was controlled continuously in real time for fast and precise positioning of a direct-drive motor. However, particle type ER fluids commonly have about 5-mili seconds response times. This delay needs to be taken into account when electric fields to energize ER fluids are controlled in real time. Especially, servo systems with ER fluid devices have a sampling time for the control loop that is about 1-mili second and so is shorter than the response time of ER fluids. Though the delay in this case has a great possibility of affecting on the performance or stability of servo systems, there is little research in this area that has mentioned the problem. In this paper, I investigated how this time delay affected damping performance and stability of this system.