Particular wirsts

[ximo_llopis]

Hi there,

I'm an engineering student, and i've been searching (googling and some books) for two particular wrists, the "triple roll wrist" and the "three roll wrist".

However I haven't found anything usefull about them.

What I need to know is the Denavit-Hartenberg or anything like that, and the possible applications for them.

If anyone can help...

Thanks

[SkyeFire]

I believe those two wrists are the same thing.

They used to be quite popular for paint robots, but I believe that they have become far less popular as robot controllers and normal wrists have improved over time. 

Hm.  There is a brief mention in Wikipedia's "Industrial Robots" article of triple-roll wrists, but their description does not match the wrists I am familiar with.

The most common wrist on industrial robots utilizes three axes which all cross at a common point, with a "bending" axis in between two "rotary" axes.  This wrist attempts to emulate the kinematics of a human wrist.  Most of the online articles refer to this as a triple-roll wrist.

My experience with what was called triple-roll wrists (which was a very long time ago), was with wrists whose axes were parallel and coincident (all on one line) when the axes were at 0 deg.   At 0 position, the wrist looked like a straight tube with two diagonal "slices" through it.  These "slices" were rotary bearings, creating a sort of 3D "wedge".  By rotating this wedge, and the regular joints behind and ahead of it, one could achieve a great deal of flexibility.  As I recall, these wrists were popular for paint robots because they had fewer singularity problems, and generated smoother motion with the more primitive path planners available at the time.  Their disadvantage was that they were slow, and tended to be less robust.  Robots these days can perform paint paths well without needing these special wrists, as long as some forethought and planning is used, so the special wrists have fallen out of favor over time.

That being said, I haven't worked in systems that used these wrists in a very long time, and even back then I only used them a bit.  So my information should be treated as out of date and possibly incorrect.

[rzapo]

you need soemthing like:
see - picture- ?
lock in Motoman robot type - painting application

[ximo_llopis]

Hi there, this is what i found first googling: http://en.wikipedia.org/wiki/Gimbal_lock#Robotics (sry about couldn't show it before). Wich, honestly, can't tell wich one is it (it is refered as triple-roll).

I'm attaching two images of the diferent wrists, one embeeded with the robot, and the other in a schema wit the trhee axes.

I'm gonna look about motorman, and i've found that kawasaki still sells them, as you said before, for hard painting work.

Thanks a lot for what you gave me, is being real usefull.

[rdixiemiller]

 The 3 roll wrists are still popular in painting applications because they allow a hollow arm/wrist for paint and air lines. Fanuc P-200's are a case in point. The arm is hollow all the way back to the axis 2/3 junction. Makes complicated moves possible without having to worry about a dressing kit.

[Jim C]

Attached is  drawing of a hollow wrist (Staubli TX Paint arm)