Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: Robot Attack on March 28, 2014, 09:01:02 AM

Title: Actuators for robot arms
Post by: Robot Attack on March 28, 2014, 09:01:02 AM

Hi All,

I am working on developing a new robot arm. It will be roughly .5 meters long, and im shooting for a max payload of ~2kg. 7 DoFs total (Spherical shoulder, elbow, spherical wrist), plus 1 DoF for the end effector itself.

I know that backlash can be a signficant problem in robot arms. I have a pretty healthy budget for this project. My question is, what sort of actuators are generally used in systems like this?

BLDC + Gearhead + Harmonic drive?
Large Stepers, no gearing, resolver to close the loop?
BLDC + Planetary + preload springs?

Anything I am missing in the above options?
What do large industrial robots use?

Thanks!

Title: Re: Actuators for robot arms
Post by: bdeuell on March 28, 2014, 07:36:19 PM

There are three common drive methods that come to mind when low backlash is required:

Harmonic drive
Timing belt (in particular the gates GT series belts are supposed to have good performance)
Ball screws

I believe cycloidal drives have low backlash as well but I do not have any experience with them

Springs can also be used to eliminate backlash but I would be concerned about the load range at which they are effective and the impact that would have on your arm.

If you can get sufficient torque without a gear reduction that will eliminate the problem but this is usually challenging in a arm where motor weight is often a concern.

Quote

BLDC + Gearhead + Harmonic drive?

If you use gearhead motor that has backlash and then stick a harmonic drive on after ther will still be backlash present however it will be reduced by the gear ratio of the harmonic drive

I believe harmonic drives are quite common in industrial robotic arms.

Title: Re: Actuators for robot arms
Post by: venturemfg on April 02, 2014, 06:33:36 AM

I am not very sure but pneumatic actuators having stroke near by 80-100 mm will be a better idea for the robot's arm for a max payload of ~2kg

Title: Re: Actuators for robot arms
Post by: jwatte on April 02, 2014, 09:12:04 AM

Pneumatics are cheaper, but less precise. If he's already worrying about backlash through a strain wave or cycloidal gear, pneumatics are probably an order of magnitude out of spec...

Title: Re: Actuators for robot arms
Post by: venturemfg on April 03, 2014, 03:27:21 AM

For payload of ~2kg pneumatic actuators are fine to work with. He can go for other precised actuators when looking to implement some more serious activity.

Correct me if I am wrong.