Newsgroups: comp.robotics
Path: brunix!news.Brown.EDU!agate!ihnp4.ucsd.edu!munnari.oz.au!news.uwa.edu.au!DIALix!metapro!bernie
From: bernie@metapro.DIALix.oz.au (Bernd Felsche)
Subject: Re: Hydraulic Manipulator Force Control
Message-ID: <CMwn41.49I@metapro.DIALix.oz.au>
Organization: MetaPro Systems, Perth, Western Australia
References: <ACC.94Mar17144147@henry.cee.hw.ac.uk>
Date: Sat, 19 Mar 1994 09:16:49 GMT
Lines: 39

In <ACC.94Mar17144147@henry.cee.hw.ac.uk>
   acc@henry.cee.hw.ac.uk (Andrew Clegg) writes:

>Are there any research groups out there that are doing work into
>position/force control of *hydraulic* manipulators ? I would be
>interested to find out what work is being carried out as there doesn't
>seem to be much published work on the subject that details the
>problems that are assocaited with hydraulically (as opposed to
>electrically) powered arms.

The technology to implement it is just complex enough to work
in most cases... the main problem in my view has been what to
do about processing all the feedback data in a timely way,
based on the huge degree of the complexity of the situation.
If you get it wrong, the actuators are almost always strong
enough to cause severe mechanical damage to the machine and/or
its environment. (Probably another reason not to let a "green"
post-grad loose on such a project.)

Still, I gather that if you make your control model good enough,
allowing for such things as joint slop, inertia during acceleration,
control fluid "flexibility" (volumetric expansion of hoses,
compressibility, fluid dynamic effects, control valve characteristics,
etc), and component deflections, you can achieve much the same 
level of control -- by very much the same algorithms -- as with 
electro-mechanical devices.

Because hydraulic delays are much longer than electro-mechanical
ones, the model used for control *must* be more complex to achieve
the same quality of control. The good news is that you get more
power and much higher sustained forces.

BTW: much the same applies for pneumatic devices.

-- 
+-----+ Bernd Felsche, MetaPro Systems Pty Ltd   ,,,     Phone: +61 9 362 9355
| | | | bernie@metapro.DIALix.oz.au             (o o)      Fax: +61 9 472 3337
| | | | 328 Albany Highway, Victoria Park  -oOO--(_)--OOo-   Western Australia 
|m|p|s| "Nur der kleine Geist haelt Ordnung: das Genie ueberblickt das Chaos!"
