Biomedical Engineering Reference
In-Depth Information
4
Design, Analysis, Fabrication,
and Testing of Tactile Sensors
Tactile sensors suitable for endoscopic applications should satisfy many criteria. Among
these criteria, the capability to grasp slippery tissue, to determine pressure distribution
and to measure the softness of the grasped object seem to be the essential and often
challenging ones to address. Present-day endoscopic tools such as graspers have rigid
tooth-like features to grasp slippery tissue (see Figure 4.1), therefore any similar device,
equipped with tactile sensors, should maintain the capability of grasping slippery tissue
reliably. Although several papers have been written on the challenges of designing tactile
sensors for minimally invasive surgery (MIS) applications, the proposed designs submit-
ted mainly accommodate forces in the order of grams and, furthermore, are unable to
determine pressure distribution [1 - 9].
This chapter presents the detailed design of two different endoscopic graspers.
Section 4.1 describes an endoscopic force sensor which is able to measure the
force along its length. Section 4.2 presents the design and prototype modeling of a
multi-functional endoscopic grasper. Both devices utilize the piezoelectric polymer
polyvinylidene fluoride (PVDF) of which a detailed description is given in Chapter
3. Both devices are designed such that they can be manufactured using conventional
microelectromechanical systems (MEMS) techniques.
MEMS devices offer competitive advantages due to their batch fabrication capabilities,
small size, improved functionality, and low cost, due to integrated circuitry (IC). The
incorporation of MEMS devices in surgical tools represents one of the greatest growing
areas of improvement in the medical sector. Not only does MEMS technology improve
surgical outcomes by reducing the incumbent risk attached to such procedures, it also
ameliorates costs by providing surgeons with real-time data about instrument force, per-
formance, tissue density, and temperature, as well as providing better and faster methods
of tissue preparation, grasping, cutting, and extraction [10].
This topic has, thus far, elaborated upon the multi-functional aspects of the tactile
sensor, together with the working principles and characteristics of piezoelectric PVDF
films as transducers. The ultimate objective, however, is to integrate this proposed tactile
sensor with existing MIS graspers, although in order to accomplish this, the current sensor
must be miniaturized.
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