A/C heads

[sweetts]

You know I often wonder if the screen industry is just void of solid engineers, with stepper motors acme shafts and actuators you could easily make a machine that could precisely move a squeegee with absolute accurate repeatable pressures and swipe speed. With the HUGE supply of open source micro controllers, motors and the like I think the cost excuse is just that an excuse to not re-engineering the old designs.  It is so much easier to time, adjust and control electronics than pneumatics in my opinion. Has there really been any huge changes in the basic design of presses? In the last 30 years Not really.

You mention the cost of engineering as an excuse but its not about the engineering costs but the ownership costs. Imagine a $100K machine re-engineered to have all actuators, stepper motors, acme shafts etc. etc. cost to the owner? Remember we print shirts very low margin stuff compared to other industries.

Cost to owner? If it's built right and maintained (electronics are easier to maintain over pneumatics) how would it be more expensive? Right off the top you can get rid of your compressor, oiler and air dryer what's that 5-6 grand?

[jvanick]

a few thoughts, as I've built a few 'open-source' controlled wood CNC routers (largest being a 4'x4')...

think of the size of a servo unit to lift a 800+ pound printing carousel straight up in a fast manner...  you're looking at several grand right here alone.

servos/drives for each head.. (I suppose you could still use the current AC motor/VFD arrangement that's become 'standard' for AC head units tho).

servo indexer (again, same as we use today)

servo print head -- at least 2 servos to raise and lower the squeegee and floodbar, plus their various drive components...  AND... while you'd have control of how 'far' they push, without some kind of force feedback controller you'd have much less control over the actual print stroke than you do by varying air pressure going to the print chopper... so your garment thicknesses had better be super consistent, and everything on your press had better be leveled PERFECTLY.

also consider the speeds we like to print at... in order to drive an acme screw at the speeds we run pneumatics at, the motors would have to be quite large... which equals more mass on the print head, which changes everything down the line.

once you have all this in place, you'll likely need a much faster plc than what's used today to communicate with all these drive components.

while I'll give it to you that electronics are easier to maintain over pneumatics, they're also MUCH more expensive to get the equivalent performance.

[GraphicDisorder]

Nothing is impossible but I just suspect you'd end up with less control than with air pressure. 

[Binkspot]

Servo lift is accomplishedd with the help of a spring floating the tables, the servo lift actually has more of a load pulling the table down. So the load is actually done with a small servo motor and dive pully system.

There are several machines that use the servo to drive the print carriage. IMO too much for a simple operation, the drive motor and prox sensors work fine. If you wanted to get fancy you could use a pinwheel type of pick up to count reveloutions to set the travel distance but again over kill for the operation.

The choppers could easily be reengineered to use one servo motor and controller per head if programmed properly. The unit would have to be able to sence load (amps) to replicate print pressure. This would allow you to fine tune the print pressure using a pressure relationship in stead of using stops like chopper knobs. The servo, sensors, controler and other components would be the high cost items. A mfg may have a few hundred dollars per head using air, a propperly configured electric system that would give the benefits of air and some would be several thousands of dollars per head. Greatly increasing the cost of a machine.

IMO a round/round press is a better machine then an up/down. The speed is faster while increasing dwell time between indexes giving more time to load and unload without sacrificing production numbers. The wear and tear on the press is much less also.

[Binkspot]

Oh and squeegee/flood locks along with screen clamp issues can be over come with a little creative engineering.

[sweetts]

a few thoughts, as I've built a few 'open-source' controlled wood CNC routers (largest being a 4'x4')...

think of the size of a servo unit to lift a 800+ pound printing carousel straight up in a fast manner...  you're looking at several grand right here alone.

servos/drives for each head.. (I suppose you could still use the current AC motor/VFD arrangement that's become 'standard' for AC head units tho).

servo indexer (again, same as we use today)

servo print head -- at least 2 servos to raise and lower the squeegee and floodbar, plus their various drive components...  AND... while you'd have control of how 'far' they push, without some kind of force feedback controller you'd have much less control over the actual print stroke than you do by varying air pressure going to the print chopper... so your garment thicknesses had better be super consistent, and everything on your press had better be leveled PERFECTLY.

also consider the speeds we like to print at... in order to drive an acme screw at the speeds we run pneumatics at, the motors would have to be quite large... which equals more mass on the print head, which changes everything down the line.

once you have all this in place, you'll likely need a much faster plc than what's used today to communicate with all these drive components.

while I'll give it to you that electronics are easier to maintain over pneumatics, they're also MUCH more expensive to get the equivalent performance.

Pricing the big 240s you can get them for 340 retail

[jvanick]

I tend to agree with bink that a screen drop vs table raise is probably the better method tho I'd you were going to go all electric.

I still think the cost of all the electronics would really add up tho and make it not cost effective.

[sweetts]

To say pneumatics will be more accurate then electric drive, to me , is silly talk.
Cheaper sure, better? Who knows none built.  I understand the economics and the increased costs but I really don't think, all things considered it would be much more over the life of the press. Obviously a home built cnc machine would not be the pricing model for building industrial equipment not even close but the open source market has lowered a lot of the electronics across the board including your larger drive equipment. Imagine if you might a press that you dial on your squeegee speed then change your inks out and it automatically adjusts, can't do that without electronics. What about a platen that senses when the thickness has changed on a print and alerts you? Gonna do that with air? The list goes on and on. Things that we all would drool over and want but no one is thinking about making, too hard too pricey, and the industry stays where it's at.

[jvanick]

Electric positioning is very accurate for getting to a repeatable place.

Force measurement on electric systems typically don't have very accurate measurement, at least ar the less expensive of the spectrum.

[tonypep]

To say pneumatics will be more accurate then electric drive, to me , is silly talk.

One could say the same for this thread

[244]

To say pneumatics will be more accurate then electric drive, to me , is silly talk.

One could say the same for this thread

agreed!

[inkman996]

To say pneumatics will be more accurate then electric drive, to me , is silly talk.

Are we running milling machines producing $$$Valuable$$$ components, or are we printing t-shirts for pocket change?

[sweetts]

To say pneumatics will be more accurate then electric drive, to me , is silly talk.

One could say the same for this thread

It's just me being silly not the entire thread.

[ebscreen]

The most common thing I've ever had to fix on any press is air valves/lines. While maybe not feasible to completely remove air,
I will say the less of it the better. Squeegee choppers would be the most difficult as you need some amount of cushion.
What about big adjustable springs, which is essentially what a pneumatic cylinder is? Sure springs wear out, but so do cylinders.
(save for the Kuhnke brand apparently)

[Gilligan]

I tend to agree with bink that a screen drop vs table raise is probably the better method tho I'd you were going to go all electric.

I still think the cost of all the electronics would really add up tho and make it not cost effective.

The boys in New Orleans have this on their 12? color... it's done pretty well.  Thought time will tell, they are certainly putting it through it's paces!