Fiber-mirror integrated compliant mechanical system for measuring force and displacement simultaneously

Measuring force and displacement in some environments is not a straight forward task. For example, in the presence of flammable materials or when surgery robots are dealing with human body, force and displacement sensors should be redesigned for this use. In surgical applications, the sensors have to be electrically passive and EMI compatible. Many kinds of sensors have been introduced for this application, namely, peizoresistive, strain gauges, etc. Although these sensors have many advantages in this regard, they are neither compatible with EMI environments nor electrically passive. So, a novel method of optical sensing need to be developed for these applications. The optical sensors may be fabricated in micro scales to overcome aforementioned needs. Some examples of optical force sensors work based on light transmission in optical fibers [1]. The proposed optical sensor is quite simple and it measures both force and displacement using only one moving object. In the proposed system, light from an optical fiber is reflected by an integrated mirror fabricated through micromachining. The light that gets coupled back into the fiber is dependent on the gap and angular misalignment between the fiber and mirror that varies with applied force and displacement. Finite element modeling of the sensor was carried out with COMSOL and optical loss was estimated for different applied forces. This paper presents the design, modeling and performance behavior of the proposed system in terms of optical loss for different applied loads.