DESIGN A SYSTEM TO MOVE A VACUUM FILTER 1

[trihydrate]

I have to design a system to move a vacuum filter, weighing approximately 200 lbs., along an overhead track, stopping at four locations along a 25 foot travel. The four stops will not be in sequence and some will be visited more than others. The system has a duty cycle of only 2 - 5%. The travel velocity is not critical, probably in the range of 1 in/sec to 6 in/sec. The position accuracy for the stops is ± 0.5 inches. The system will operate unattended, although I plan on having cameras mounted with the equipment that will enable me to "see" the equipment, via modem, in operation periodically. The typical service call to correct, repair, or adjust will be approximately 200 miles one way.

I would like to have input as to: 1. The "best"(most reliable) motive system to use. 2. The "best"(most reliable) position sensing sysem to use. 3. Any "traps" to avoid.

Thanks for any comments you might have.

 

[schick]

travelling that far, my first thought would be to use an electric motor connected to a plc and a freq drive. use a binary setup to label each of the 4 locations so you could adjust your program go directly to any one, in any order.

as far as positioning, you could use a optical sensor, but that means having to reset to your datum each time the system powers up.

Don't have much experience with relatively long distance travelling machinery (over a couple of feet).

Good luck.

 

[NRT]

I think you need to think in terms a garage door opener. The track length is a little more than twice the length of a garage door system. Positioning is controlled by simple and reliable switches, manually located along the track to stop the movement at the same position from either direction within your plus or minus 0.5 inches. The 200 pound load can be carried by a wheeled-guided track that is not attached to the drive system, thus allowing a small electric motor to provide the motion you need without having to carry the load on a chain or acme screw. You probably will not want a lot of speed, since the inertia involved in starting and stopping a 200 pound load ( the weight of some wood panel garage doors) may affect your ability to meet your positioning accuracy.

 

[ferreiro]

Hi,Have you thought of gear drive with plc memory and sensors.The gear drive will handle the 200lbs and you can design the gears to suit the spacing requirements.Each sensor can have a different address on the plc program thus you would be able to tell it where to go
tks
robert

 

[GregLocock]

1) The most reliable power system will be an oversized electric motor, since any other practical primemover will need an electric motor to pressurise it, or rely on combustion, which is inherently less reliable.

2) The most reliable position sensing system is probably an optical system . I suggest you set 4 detectors at different heights on the carriage so that there is no ambiguity in station position. Decelerating from 1 in/s in 0.5 in will require an acceleration of 1 in/s/s, not exactly stressful. Mechanical limit switches are fine, but have a nasty tendency to misbehave a few times until they are correctly installed and shielded.

3) If you want to go for a high up-time and long maintenance intervals then you could use a redundant sensor system. If high reliabilty is your #1 consideration then a 25 foot long square drive, with the carriage on a rack, is probably the most reliable solution.

Cheers

Greg Locock

 

[StevenCPotter]

At a speed of 1"/sec. with 200lb load I think inertia of stopping to +/- .5" would require either massive amount of bracing or, or (preferably) a time delay to allow the filter to settle down when drive motor is disengaged. Depends on how you support it, backlash in gearing and chain, etc. Steven C. Potter
steven@canadastainedglass.com

http://www.landrower.com

"80% of success is showing up." -Woody Allen

 

[GregLocock]

Well, 1 in/sec/sec is less than 0.3% of a g, so it is not exactly a crash stop. Cheers

Greg Locock

 

[trihydrate]

GregLocock,

I appreciate your response and your consideration of the up-time and long maintenance intervals. I'm currently looking at an AC motor, gear reduction, a pinion and a rack for the carriage to run on. Redundant optical sensors will be used for position control. The one thing I don't understand is the term "square drive". I appologize for my ignorance, but I would appreciate a bit of clarification.

Thanks so much for your help.

Trihydrate

 

[GregLocock]

If you look at the power drive for the cross slide on some lathes you'll see what I mean.

Basically have a square section shaft running the length of the rail (Oh, 25 foot is a bit much unsupported, but the idea may still help).

Turn this with your motor and gearbox, then simply have a square nut to pick up the drive, and a gearbox to get the drive to a rack and pinion.

Well, overall that sounds more complex than your proposed setup, and I can't see how to support a 25 foot rotating square drive.

I think you have chosen a sensible architecture - getting the power to your motor is going to require a bit of thought, but all the sensors can be carried on board the moving trolley, so that simplifies the control side of things. Cheers

Greg Locock

 

[trihydrate]

GregLocock,

I hadn't heard the term "square drive" before and your example of the cross slide power drive on a lathe finally hit home. Some of us Texans need positive reinforcement, sometimes applied with a ball bat. Seriously, in my neck of the woods, the most common name of that form of power drive is "Acme allthread". From now on though, I will not flinch when I hear the term "square drive".

Thanks again for your help and patience with me. I'm anxious to get this designed and built.

You have been a big help, Good Luck!

Trihydrate