Re: [CAD_CAM_EDM_DRO] Re: hydraulics with CNC

Hi guys;

Part of the problem is residual pressure/movement. In a pneumatic system the
medium is compressible,which adds to the problem; Liquids don't compress.
What that comes down to, is that when you move the ram, and then cut off the
pressure/flow at the valve, there is still some pressure in the system, which
causes a small but definite additional movement of the ram. This varies with
the resistance the ram sees at various positions within the cylindar, so the
amount of additional movement at any given position can problematic. You can
stop the movement with a brake of some sort, or with valved back pressure, but
this still requires a small amount time to apply the brake, or for the back
pressure to build up to an adequate level. Proportional valves improve the
picture quite a bit, but I wouldn't expect an extreme amount of accuracy from
such a system. This doesn't account for the weight and mass of the table,
workpiece, fixtures, jigs, or whatever else. None of that means that your
machine is useless, but from the discription so far, it sounds like it would
build a better locomotive, than it would a motorcycle.

Bill

On Mon Jun 7 08:32:38 2004 cnc002@... wrote:

>In a message dated 6/7/2004 11:18:59 AM Eastern Daylight Time,
>eexgs@... writes:
>
>I wonder if some
>simple electronics could be made so that the hyraulic ram would act
>like a stepper. In other words a step pulse comes in and the ram in
>turned on until a certain number of pulses have been received from
>the encoder then it is turned off. Assuming you don't send the
>pulses too fast it would work OK. It also assumes that the ram
>doesn't need true servo control to hold it in lock.
>
>Just a thought, don't know enough to say much more.
>
>
>I must have missed the original post on this. Is the application one where
>you wish to position a hydraulic piston in specific locations but not the
>full travel each time. You want to be able to stop it at various locations I
>assume. There are special valves for this purpose, they keep the pressure
>constant on each side of the piston until a move is called for and then they
>release the pressure on one side and apply it on the other until told to turn
>off. Then the fluid pressure is applied, again, equally on both sides of the
>piston. This holds the piston in the existing position. I haven't used these
>in a hydraulic application but have used them in pneumatic applications but,
>I was using a linear encoder for feedback so that the control knew when to
>turn off the signal. I don't see why you couldn't do the same thing with a
>stepper, just control the number of pulses as mentioned.
>We used Keystone pneumatic valves and solenoids on these projects and I
>don't know if they even make a hydraulic version but I would think someone, like
>Parker, would make control valves of this nature.
>Randy Abernathy
>4626 Old Stilesboro Road NW
>Acworth, GA 30101-4066
>Phone / Fax: 770-974-5295
>Cell: 678-772-4113
>E-mail: Cnc002@...
>
>I furnish technical support, repair, and other related services for your
>industrial woodworking machinery. My background as Senior Service Engineer for
>the SCMI Group for nearly fifteen years with factory training, combines with
>my extensive background in electronics, mechanics, pneumatics, electrical and
>CNC machinery to offer you needed support for your machinery.
>
>
>[Non-text portions of this message have been removed]
>
>
>
>Addresses:
>FAQ: http://www.ktmarketing.com/faq.html
>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
>Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
>Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@..., timg@...
>Moderator: pentam@... indigo_red@... davemucha@... [Moderators]
>URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
>OFF Topic POSTS: General Machining
>If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble.
>http://www.metalworking.com/news_servers.html
>
>http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.
>
>NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
>bill
>List Mom
>List Owner
>
>
>Yahoo! Groups Links
>
>
>
>
>
>

--
********************************************************************************
* *
RKBA! * Blessings on thee, oh Israel!!! * 4-19!
* *
********************************************************************************

An _EFFECTIVE_ | Insured by | All Matter is vibration. | Let he who hath no
weapon in every | by Colt; | --Max Planck | weapon, sell his
hand = Freedom | Dial | In the beginning was the | garment, and buy a
on every side!! | 1-911-A1 | Word. --The Holy Bible | sword. --Jesus Christ

********************************************************************************

Constitutional Government is dead! LONG LIVE THE CONSTITUTION!!!!!!

********************************************************************************