adaptive robotic arm

[larrylart]

Hi everybody,

I built myself a robotic arm fitted with a 4dof gripper a camera, slip and touch sensors:

http://larryo.org/work/robotics/robotics_hardware.html

I am also developing a software (chorg) to process real-time video and provide adaptive control of the arm.
So what do you think of it?

Larry

[Admin]

post some video!

what would you say is the most difficult part of the project?

what parts of the project arent up to your spec and you think needs improvement?

why did you choose to mount the camera on the arm instead of on the base mount?

curious . . .

[larrylart]

Hi Admin

post some video! 

I had 2 videos two videos around with the arm perfmong two different tasks  but I don’t know what I did with them … I will to make some videos with another webcam because my dv camera is currently in bits - in an  effort to adapt it to the arm I snapped one of the flexible cables – anyone has any idea how to fix such thing ? other then just reroute some 20 paths with separate wires ?

what would you say is the most difficult part of the project?

By far that was the mechanical part – specifically the gripper construction. Also challenging was to counterbalance the arms weight with springs and to put together/tune the slip sensor on the gripper.

what parts of the project arent up to your spec and you think needs improvement?

On the mechanical side I plan to replace to current tubular structure with rectangular shaped bars – that will give me better rigidity, more space for cables/electronics and provide a better heat dissipation medium for servos.
Also, I will like to replace the camera – I need a camera with high-speed auto-focus functionality. First I thought of using a dv camera the only issue is that most are to big for this arm – sure you can strip them apart and re-position the electronic in different parts of the arm – but then again that would mean even more cables around. Then I though of using a modified commercial digital camera which will also provide me with the ability of talking hires snapshots (which will help a lot with the ocr engine) – I will have to decide which is the best (size/quality/auto-focus speed) and it will be great if it has also an sdk available (like canon has).
I will also like to add another interface in the base to measure how much current every servo draws (or at least two of them at the shoulder and elbow) and use this to calculate the torque.

why did you choose to mount the camera on the arm instead of on the base mount?

I tough of that initially – having the camera on the base has some advantages – such as it could provide feedback more easily on the proximity to an object relative to the arm. On the other hand, if the camera moves with the arm gives it the capability to better analyze (close up) the object position, shape and/or read labels/bar codes which might not be properly visible from a fixed position.

Larry

[Nyx]

What kind of motors do you use to move the arm? And how much weight can it lift? I would like to build something similar for my mobile robot.

[larrylart]

I use 10 standard rc digital servos: 5 x HSR-5995TG for the arm, 1 x HS-5445MG for the wrist rotation and 4 Saturn DS50M for the gripper.

It can lift up to 1kg more or less - it depends on the strategy/constrains of the task.

Larry

[robot321]

Reading this thread brought to mind of something I don't think that has been discussed on this site about robot grippers.  Or maybe I missed it.

Friction Grip vs. Encompassing grip. Like a 4/1 ratio.  Something to think about.

See : http://www.grippers.com/size.htm

[Nyx]

I use 10 standard rc digital servos: 5 x HSR-5995TG for the arm, 1 x HS-5445MG for the wrist rotation and 4 Saturn DS50M for the gripper.

It can lift up to 1kg more or less - it depends on the strategy/constrains of the task.

Larry

So you use several servos to rotate one joint of the arm?

[larrylart]

So you use several servos to rotate one joint of the arm?

Yes, I use two for the shoulder.

Friction Grip vs. Encompassing grip. Like a 4/1 ratio.  Something to think about

True, on top of that it’s very important the frictional coefficient of material used to pad the gripper. I used a tick/soft rubber layer made of mouse pad and it seems to work fairly well – even for the touch sesors.

Larry

I use 10 standard rc digital servos: 5 x HSR-5995TG, 1 x HS-5445MG for the wrist rotation and 4 Saturn DS50M for the gripper.

It can lift up to 1kg more or less - it depends on the strategy/constrains of the task.

Larry

[Admin]

Also challenging was to counterbalance the arms weight with springs and to put together/tune the slip sensor on the gripper.

Yea I had the same problem. I had to mount all my batteries (the yellow things) as counterweights on this robot arm . . .
http://www.societyofrobots.com/images/materials_HDPErobotarm.jpg

My gripper worked with only one redesign for that arm.

(btw, my robot arm could deal out playing cards to four people around a table . . . ill document it one day . . .)

The other gripper I did was for this robot:
http://www.societyofrobots.com/robot_asme.shtml
If you look at the bottom pic, you will see our first gripper version. It was made out of black plastic, and it quickly broke . . . challenging stuff!


as for your servo overheating problem . . . not sure how to help you there . . . have you considered using a worm gearing for the servos at the base? if the arm isnt moving, the servos wont need to apply a holding torque.

[larrylart]

as for your servo overheating problem . . . not sure how to help you there . . . have you considered using a worm gearing for the servos at the base? if the arm isnt moving, the servos wont need to apply a holding torque.

Yeah, using a worm gearing is great idea – unfortunately I don’t think it will solve the problem, as the tasks I have in mind require continuous movements over long periods of time.   Ahh well … for now the heat sinks are doing ok and in next version there I should have an better heat dissipation.
However, adding a worm gear might help reduce the stress/wearing on the servos gearbox … trying to picture in my mind how that can be implemented at the joint level…

Larry