Flex sensor

This arm rehabilitation monitoring device consists of a flex sensor, a Microchip PIC18F4520 microcontroller, a Cytron SK40C PIC start-up kit, a USB to USART converter, a USB ICSP PIC Programmer and a 16x2 RT1602C LCD display. Figure 1 shows the actual hardware setup. 

Flexible sensor or flex sensor is a type of resistor which actually composed of tiny patches of carbon that can change resistance values when bending from convex to concave shapes. It is known as an ideal input device for controlling limb-like mechanisms due to its ease of positioning when attached to finger or elbow to track movement. Figure 2 shows the basic function of flex sensor. 

In this project we will use flex sensor produced by Spectra Symbol. Resistance value of the sensor is about 8,000 2 (8K) at 0°. The resistance will gradually increase if the flex sensor as being bent inward. At 90°, the resistance value is about 10-14K 2. The flex sensor may be bent greater than 360° depending upon the radius of the curve, this will further increase the resistance value to increase more further. Its life cycle is more than 1 million bend. The sensor measures Va inch wide and 4 lA inches long and only. 019 inches thick. 

Fig. 5 (a) Elbow guard attached with flex sensor (b) LCD displays repetition counter. 

In this paper, the characteristic of flex sensor has been recorded. The flex sensor is a resistance-varying strip that increases its total electrical resistance when the strip is flexed in one direction (in the other direction the resistance does not vary significantly). This angle is measured between the two tangent lines at the ends of the flex sensor s body. The flex sensor has a typical electrical resistance variation when flexed or bent as shown in Eig. 6 (a), Eig. 6 (b) and Fig. 6 (c). 

Erom the experiment, resistance value against the flex sensor bending angle can be plotted as shown on Eig.7. The experiment shows that when flex sensor is bend inward, resistance value increased significantly as the angle of flex sensor is bend further. However, when it is bent outward, the resistance value decreased gradually. These preliminary... 

Fig. 7 Resistance value against flex sensor bending angle...

Keywords— Artiflcial hand gripper, flex sensor, rehabilitation and medical robotic. 

In this section, we will demonstrate the measurements results for the mechanical part of the hand gripper by using flex sensor (refer Figure 6). Next, followed by the graphs produced for the bending analysis of the flex sensors positioned at the leather glove[9]. 

Fig. 6 Picture showing the glove sense mechanism, fingers and the flex sensors positions...

This project uses leather glove with flex sensors placed on the style of the four index fingers. The flex sensor will produce an output of lOKQ at (P and 9.56KQ at 90 . 

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