sensor to identify shapes

[minu.grg]

I am making a prosthetic hand for a competition. For that i have to solve a task with that hand. The task is to identify 3 shapes(square, cylinder and ball) with out seeing that. The size of the items will be in between 50 to 60mm for the side or as the diameter. As per the rule i cannot use a camera. Is there any sensor to identify all these shapes. The sensor should be firmly attachable to the hand without disturbing the normal activities of the hand.

 

[gophert]

Yes, you measure the angle of each finger when the object is grasped. If all grab at the same angle, cylinder, if the end fingers have little to grab and it gets thicker to the center, it is sphere,... you have to EXPERIMENT to get to the answer.

 

[minu.grg]

May i know which kind of sensor i can use for angle measurement?

 

[rjenkinsgb]

May i know which kind of sensor i can use for angle measurement?

The simplest is just a potentiometer in each joint, connected to an analog to digital converter.

Or something like this, with a direct digital position output and 1/65536 of a turn resolution...

https://docs-emea.rs-online.com/webdocs/12cd/0900766b812cdcaf.pdf

Or an incremental encoder on the servo motor, plus a way of finding the fully open "zero point".

Or pressure sensors on the finger tips (or in the joints), so you can use a cheap model RC servo and find the position that triggers the pressure switch by gripping slowly until it is triggered.

 

[minu.grg]

potentiometer in each joint? how it works?

 

[gophert]

potentiometer in each joint? how it works?

Mount the potentiometer co-axial with the pivot of each joint and the motor will move it (changes resistance) as the motor moves the joint. Apply ground and logic huh voltages to the two static pins and connect the wiper pin to an ADC input on your microcontroller. The changing voltage means changing angles. You will need to calibrate each joint on each finger to understand straight, slightly bent or completely bent values on the ADC. Lots of wires and lots of fun. Or, you can go for a more universal approach. Use a main tendon in the forearm of your bot to pull and cause all fingers to close. Measure the distance you tightened the forearm tendon to determine how "closed" the hand is. Lots of ideas, fun to experiment.