###### Abstract  
In the CCD-based fine tracking optical system (FTOS), the whole disturbance suppression ability (DSA) is the product of the inner loop and outer position loop. Traditionally, high sampling fiber-optic gyroscopes (FOGs) are added to the platform to stabilize the line-of-sight (LOS). However, because of the FOGs' high cost and relatively big volume relative to the back narrow space of small rotating mirrors, we attempt in this work to utilize a cheaper and smaller micro-electro-mechanical system (MEMS) accelerometer to build the inner loop, replacing the FOG. Unfortunately, since accelerometers are susceptible to the low-frequency noise, according to the classical way of using accelerometers, the crucial low-frequency DSA of the system is insufficient. To solve this problem, in this paper, we propose an approach based on MEMS accelerometers combining disturbance observer (DOB) with triple-loop control (TLC) in which the composite velocity loop is built by acceleration integration and corrected by CCD. The DOB is firstly used to reform the platform, greatly improving the medium-frequency DSA. Then the composite velocity loop exchanges a part of medium-frequency performance for the low-frequency DSA. A detailed analysis and experiments verify the proposed method has a better DSA than the traditional way and could totally substitute FOG in the LOS stabilization. M +
Footnote †: journal: Sensors  
1  
class=MSC] [Primary ]60F10,  
to the back narrow space of the small rotating mirror, and consume significant power to precisely control their fiber-coil temperatures, which limits their utilization. With the development of the micro-electro-mechanical system (MEMS) industry, the performance of inertial sensors, such as MEMS accelerometers and gyroscopes with small size, low weight, low cost and low power consumption, especially accelerometers whose bandwidth could reach 1000 Hz, has improved a lot [12; 13]. However, since the MEMS gyroscope's bandwidth usually doesn't exceed 100 Hz, so it is unable to substitute the FOG alone whose bandwith is about several hundred Hz in FTOS. Therefore, In 2016, [PERSON] combined a MEMS gyroscope with a MEMS accelerometer to construct a triple-loop control (TLC) which includes acceleration, velocity and position loops to enhance the DSA and succeeded in making the whole DSA equal to the traditional way [8]. Nevertheless, in the space limited occasion, the rotating mirror is too small to install two different sensors, so we try to use only a sensor, obviously only the high-bandwidth MEMS accelerometer has the potential to substitute the FOG in the system. Since [PERSON] and [PERSON] firstly introduced accelerometers to the feedback control system [14], more and more researchers began to use accelerometers in precision control field [12; 15; 16]. In 2009, [PERSON] introduced the accelerometers to FTOS. As accelerometers are susceptible to the low-frequency noise, he designed the acceleration closed loop to be a band-pass filter to guarantee the system's stability, which resulted in its insufficient DSA in low frequency compared with the traditional VDLC way [17]. However, the DSA in low frequency is crucial for the system, because in most occassions the low-frequency and medium-frequency disturbance is primary. In this paper, in order to enhance the DSA with accelerometers, we propose an approach based on MEMS accelerometers combining the disturbance observer (DOB) built in the acceleration loop with TLC in which the composite velocity loop is built by acceleration integration and corrected by CCD. Since the low-frequency disturbance observed by DOB is not accurate because of accelerometer's noise and the model of FTOS is not fully matched with the real platform at high-frequency, we use the DOB method mainly to greatly improve the medium-frequency DSA. Then, we try to add a composite velocity loop to improve the low-frequency DSA, whose difficulty is how to acquire the velocity without gyroscopes.