BioInstrumentation
Fingernail Force Sensing
While the human hand is grasping or pushing on an object, there is a force applied to the object and equally to the tissue of the palm and fingers of the hand. This force deforms the tissue and can cause blood vessels to begin to collapse and allow blood to accumulate in different areas. This is easily observable under the fingernail. As you apply force to the fingertip, you will notice areas of the fingernail become a darker shade of red, while other areas become more white. This is where the blood is accumulating and evacuating respectively. As the magnitude and direction of the force change, the distribution of the fingernail will also change. The goal of this research is develop a sensor that can use this blood / color distribution to create non-invasive haptic force sensor that will not imping on a subject's sense of touch.
We are currently exploring two method for mapping the blood/color distribution of the fingernail. The first method is to take a complete image on the fingernail and completed series of image processing, this research is being done in conjuntion with John Hollerbach. The second method is take use a series of photodetectors in a fingernail size sensor to examine the light reflected off of the fingernail. Both methods have their advantages and disvantages. The image processing method can have very high resolution, but requires significant processing power and it is difficult to locate the camera directly above the fingernail at all hand positions. The fingernail sensor can be easily be attached to the fingertip and the orientation of the fingernail is not critical, but the resolution of the senors is limited by the number of photodetectors.
Fingernail Sensor
The two fingernail sensors are located on the index and middle fingers. The sensor are constructed on PCB with surface mounted LEDs and photodetectors. The palm side of the finger does not have anything on it, allowing the subject to have full sense of touch. The glove and straps are only used for securing the cables to the hand.
