## 4 Experiment Preparation
### Experimental Method  
As shown in the Figure 7, the whole experiment system contains eight parts, including the host PC, real-time system, motorbike, servo actuator, embedded servo controller, transducer, IPE signal conditioner and embedded data acquisition.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Name** & **Value** & **Dimension (Remark)** \\ \hline Experiment duration & 199.68 & s \\ Drive frequency & 1000 & Hz \\ Sampling frequency & 1000 & Hz \\ Servo valve type & Moog \&761-3010B & (2 stage servo valve) \\ Hydraulic actuator type & R-ZD-0020-0200 & (Symmetrical cylinder) \\ Accelerometer type & B\&W Tech. 14100 & (IPE) \\ Motorbike type & Sanlg SL125-2E & (Lightweight motorbike) \\ Hydraulic oil Pressure & 2.1 & MPa \\ Transducer limit & \(\pm\)500 & m/s\({}^{2}\) \\ Transducer accuracy & 0.001 & m/s\({}^{2}\) \\ Transducer bandwidth & 0.2–10000 & Hz \\ Motorbike tire pressure & 150 & kPa \\ Motorbike wheel base & 1.350 & m \\ Motorbike total mass & 83.35 & kg \\ Motorbike barycenter & 0.732 & m (Horizontal distance from front axle) \\ Front sensor location & 0.351, 0.542 & m (Horizontal, vertical distance from front axle) \\ Controller P parameter & 0.75 & A/m \\ Controller I parameter & 0.05 & A/(m*s) \\ Controller D parameter & 0.0005 & A*s/m \\ Control accuracy & 0.02 & mm \\ Gravity & 9.794 & m/s\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Experiment parameter list.  
Figure 5: Test bench.  
Figure 6: Block diagram of experiment system.  
The host PC is used for iteration calculation and monitor, as well as sending drive data to real-time system and receiving response data from real-time system over the ethernet. The real-time system is used for real time control and data processing, as well as exchanging data with the host PC over ethernet as well as with the embedded servo controller and embedded data acquisition over the field bus.  
The servo actuator contains a servo valve, symmetric actuator and LVDT used for displacement measurement. The controller and the servo actuator form the displacement closed loop, to make sure that the iterative displacement drive is accurately generated and applied to the wheel of the motorbike. The motorbike is the device under test and driven by the piston of the actuator.  
The transducer is an IPEE accelerometer, mounted on the body of the motorbike by neodymium magnet, and used to measure the vertical acceleration of the motorbike as the response of the iteration. The IPEE signal conditioner is connected with the sensor by coaxial cable (coax. for short) to stimulate the sensor, to amplify and filter the signal collected, and then it transmits the adjusted analog signal to the data acquisition equipment over the STP (shield twisted pair). The embedded data acquisition is used to collect analog signal transmitted by signal conditioner and carry out A/D (analog to digital) conversion, and then transmits the digital response signal to the real-time system over the fieldbus.  
The whole system is based on real-time control and synchronous sampling technology, so the time difference between control and sampling is less than 10 microseconds, which ensures the accuracy of experimental control and sampling phase. The control and sampling time difference of the experimental equipment has no relation with the natural frequency of the system. Because according to our experience, when the control and sampling time difference of experimental equipment changes greatly, for example, if it is greater than 1 millisecond in this experiment, and it fluctuates in each iteration, then the error of system TF estimation will occur due to the change of phase difference between input and output, so that the iteration may diverge. The time difference within 10 microseconds is satisfactory, and the interference caused by this factor is not needed to be considered in the whole iteration process.