Now that my 6 DOF robot arm is assembled and tested, I thought it would be
nice to get working on the first technique I need to understand: haptic control.
Haptic : Of or relating to the sense of touch; tactile. [Greek haptikos, from haptesthai, to grasp, touch.]
The basics of haptic control:-
1. Sense the movements of the human body
2. quantify these movements into electrical signals
3. control robotics with the electrical impulses
The simplest way to sense movement of fingers – perhaps in a “gripping” application is by using a flex sensor or a bend sensor. Flex sensors change their electric resistance as they are flexed and can be stitched into gloves and sense the moments of the human fingers within the glove.These electrical signals can be transformed into motion on a robot.
Unfortunately, unlike most of the electronics I have been working with, flex sensors are prohibitively expensive, a small 7 cm sensor (like the one shown below) can cost nearly US$ 17 – 23. Multiply this by five (one for each finger) and a haptic control glove can easily run up to US$ 100 – 120.
Luckily for me, there are some clever people who have found a cheap and easy way to build flex sensors and are kind enough to share their knowledge for free. I found that these plans worked perfectly. They were easy to follow and in less than 15 minutes, I had one working flex sensor.
All I needed was a conductive plastic bag(anti-static bags), cello-tape, electrical wires, and a cable tie. Total cost – hardly anything. Playing around with this sensor, I found its resistance varied from about 6Kohm (bent fully) to 30 Kohm(extended).
To put this into use in a robotic application, I placed the flex sensor into a voltage divider and mapped the output voltages to values between 90 and 180 (These are the angular limits of the servo on my robot claw). Here is the video of the sensor at work.
Cheap, easy to make, and works great.