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Author Topic: sensor for relative position of parts of robotic arm  (Read 522 times)

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Offline sreenathvTopic starter

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sensor for relative position of parts of robotic arm
« on: January 12, 2014, 09:26:48 AM »
I am doing a project on robotic arm. I bought OWI Robotic Arm Edge- http://www.owirobots.com/store/index.php?l=product_detail&p=110

 I want it to pick things based on colour automatically. I want the arm (the different parts of the arm)  to be at a default position at the beginning and want it to comeback to the same position, the parts. The arm as a whole is not moving. What kind of sensor can I use to do this, find relative position of various part of arms. A sensor that i can fix at various parts of the arm and measure the distance moved by each part or relative position between the parts.I cant use encoders on motor to measure the distance from rotation because of the assembly of the arm.

I would also like to know what kind of sensor can I attach to the gripper to know when it touches something - a pen for example.

Offline bdeuell

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Re: sensor for relative position of parts of robotic arm
« Reply #1 on: January 12, 2014, 01:48:58 PM »
An encoder does not have to be placed on the motor it can also be placed at the joint ... is this possible? Potentiometers might be a cheaper option than encoders if you can place them at the arm joints.

For the contact sensor of the griper you could look at using a thin film pressure sensor. Here is one from sparkfun https://www.sparkfun.com/products/9375. You could also measure the current drawn by the gripper motor tho determine when the motor has stalled or applied sufficient pressure to the gripper.

Offline CJAlbertson

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Re: sensor for relative position of parts of robotic arm
« Reply #2 on: February 04, 2014, 11:27:42 PM »
I am doing a project on robotic arm. I bought OWI Robotic Arm Edge- http://www.owirobots.com/store/index.php?l=product_detail&p=110 .... What kind of sensor can I use to do this, find relative position of various part of arms...



You will need to need creative.  For example you can hot glue a plastic disk to one pat and an optical sensor on another.  Just the other day I found I could use normal "perf board" and a slotted optical switch the holes in the paperboard where detected.  Linear sensors are not so hard to make and you cn use a microswitch to find a"home position.

People have also mounted gyros and accelerometers on the various parts of the arm.  As it turns out if you use cheep home made sensors you should use more than one and then you gain great precision when you "fuse" the data even if each sensor by itself is not so good.   You can also get some idea of the position by looking at the motor current because torque s needed to overcome gravity.  More power is needed in some poses.   Combine all of this.  When you multiply several high signal measurements you get a low sigma result.
Chris A. in So. Cal.

 


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