stepper motor / PC control of emulsion making

[Kirk Keyes]

From what I am reading on this forum, it seems like the process of emulsion making on a small scale would benefit tremendously from using small stepper motors, servos, solenoids, etc (machine control) to keep certain steps in this process more exact and repeatable.

This thread is fun. I thought I would bump it. It's been a year - Anyone have any other thoughts on the subject.

 

[Photo Engineer]

You know I do Kirk!

I am about to embark on that for the second part of the DVD.

I have peristaltic, diaphragm and centrifugal pumps for this purpose.

TaDa!

PE

 

[Kirk Keyes]

Well, I knew you did. I meant the others involved or new to this type of endeavour.

 

[Kirk Keyes]

And how did I miss this entire thread until now! I guess I was getting ready for your class last year...

 

[ben-s]

I've kind of gone off the boil on this side of things at the moment.
The cost of setting up such a system without having ready access to the knowledge needed to run it without generating a lot of expensive gloopy mess is too high for me at the moment.
While automated systems can have huge benefits, to quote an old colleague of mine, "Automated machines can generate scrap at an astonishing rate"

However, if I can help anyone with the automation side of things, please shout and I'll do what I can.

 

[Photo Engineer]

Ben;

I'm making emulsions right now that are repeatable and good in speed and curve shape (Except when I goof myself like adding the wrong gelatin recently!). Once you get a good emulsion with a syringe as I am doing, then the pump only increases quality.

You can get good pumps for about $75 US, and I control one of them with an electric train transformer to give me the exact sped I want. Simple, efficient and higher quality .......

PE

 

[Kirk Keyes]

I think a lot of the discussion here was aimed at making a syringe pump - but it looks like no one here has any experience with commercial versions of them, or with peristaltic pumps. Personally, I think peristaltic pumps are the better choice, as you have a lot of flexibilty with them simply by changing the diameter of the pump tubing. And since a lot of them are multichannel, you can pump more than one thing at a time. And you can have them pump things at different rates by having multiple diameters of tubing.

Pumps can be found for $50 and up. Same with syringe pumps. I guess either one works for smaller volumes, but I have a feeling a peristaltic pump will give more even flow and with less pulsing than a syringe pump. I've never used a syringe pump, other than seeing the in operation in the hospital, so those are just my feelings.

Also, peristaltic pumps are not limited in the total volume dispensed, as a syringe pump is limited my the size of syringe they hold.

And for computer control, many newer peristaltic pumps are digitally controlled - no need for train transformers. (Not that there's naything wrong with that...) You simply punch in the speed you wond on the display, and off they go. And they usually have a serial port so you can have a computer control them if you like.

 

[Photo Engineer]

A good centrifugal pump produces no pulsations and can cost as low as $50 - $100, a peristaltic pump produces pulsations unless precautions are taken and the pumps run in the range of $700 - $2000. A syringe pump produces no pulsation and can cost up to $10,000. They are the most accurate, but hardest to maintain and clean. The peristaltic pump is the easiest to clean.

They all have advantages and disadvantages, but the syringe pump is the most limiting of them all IMHO. The computer controlled versions with digital readout on the front panel are quite expensive. I'm trying to make this as inexpensive a proposition as possible, but hope to show the top of the line equipment possibilities as well.

PE

 

[Kirk Keyes]

Reducing pulsing on a peristaltic pump, or any pump for that matter, can be handled by adding several feet of tubing after the pump before the dispensing end of the tubing. I assuming we are talking delivery rates of a bit less than 1 to a maximum of 5 ml/minute or so? If that's the case, then a meter or so of 24 or less guage tubing will reduce the pulsing. And the dead volume of tubing that small is quite small itself, but it has a lot of drag on the liquid being pumped.

 

[Kirk Keyes]

Ebay has several syringe pumps that have sold for less than $100 recently. I don't know who flexible they are in adjusting flow rates. That's what I like about peristaltic pumps - they are generally very flexible.

PE - do you have any centrifugal pumps you can recommend trying?

 

[Photo Engineer]

Kirk;

Long tubing means long overrun to clear the lines and the possible retention of solution. I have another way to control this problem that will be made clear in the DVD.

As for pumps, try the Flotec 12 V marine pump. It runs much too fast, as is, but stepped down to about 5 V it runs right in the range we want and delivers the right volumes spot on. It is much less than $100. And, BTW, this can be used for the UF washing and will reduce overall costs there by nearly $1000. It does take very careful monitoring though as a UF unit.

PE

 

[Kirk Keyes]

Flotec - I've heard of them. I'm planning on using one of their sumps for my darkroom in the basement some day. But I can't find any "marine" pumps on their site - http://www.flotecwater.com/

Can you give a part number?

A meter of really big delivery tubing (at least for me) of say 1 mm diameter has a dead volume of 0.75 ml. A meter of 24 guage tubing, which I'm using has a dead volume of 0.2 ml. That's not much dead volume. And add a squirt of water to the reservoir as the last drop is pumped out and let that rinse the tube if needed. Or let the pump push some air through for a few seconds.

 

[Photo Engineer]

Kirk, All;

I gave out the wrong pump name and company. Sorry. You can find it here:

http://www.shurflo.com/pages/Food_Service/water/categories/reverseosmosis/goldseries_RO_pumps.html

I have pump model # 8875-142-313

I have so many here, I somehow got the wrong one for posting.

PE

 

[Kirk Keyes]

SO that one does 100 gpd, which is a bit over 250 ml/min. That's still a bit more than needed to deliver silver nitrate into a beaker for home use. I'm sure it works fine, but I think I'd be nervous about lowering the supply voltage as it might severely shorten the live of the pump. Unless they are designed to run at lower voltages...

I still think a peristaltic wins for flexibility in delivery rate.

 

[Photo Engineer]

Kirk;

That is at 24 volts. I control it with a variable AC transformer and at 7 volts it does very well indeed. After all, what other uses can you make of old Lionel or American Flyer transformers except to run your trains.

PE

 

[Neanderman]

About all I have to offer is that I still have a peristaltic pump sitting in my cube at work, waiting for delivery to the darkroom. (It's a hassle parking blocks away from the office...) But I look forward to playing with it!

Ed

 

[Photo Engineer]

And I just spent nearly 1 hour finishing off the DVD portion on peristaltic pumps.

PE

 

[Photo Engineer]

Dual pump delivery system

Here are two quick load heads on a Masterflex pump set up to deliver silver nitrate and salt solution at equal rates to a making kettle.

This dual run can approximate a controlled vAg environment without computer control and can give highly uniform emulsions.

PE

 

[Photo Engineer]

Calibration

Once you have a pump, you must calibrate it in terms of voltage (potentiometer reading) or RPMs (timing rotations) and measure the output in milliliters.

This is a calibration curve of the Masterflex pump shown above. The two lines show the curve for both heads pumping distilled water.

Every pump head and tubing combination must be regularly calibrated to insure exact flow rates. And, as tubing ages, the flow rate, due to softening of the tubing, changes gradually. Tubing under the rollers of a peristaltic pump must be flexible and must be replaced regularly.

PE

 

[Ray Rogers]

Once you have a pump, you must calibrate it in terms of voltage (potentiometer reading) or RPMs (timing rotations) and measure the output in milliliters.

This is a calibration curve of the Masterflex pump shown above. The two lines show the curve for both heads pumping distilled water.

Every pump head and tubing combination must be regularly calibrated to insure exact flow rates. And, as tubing ages, the flow rate, due to softening of the tubing, changes gradually. Tubing under the rollers of a peristaltic pump must be flexible and must be replaced regularly.

PE

Interesting...
How do you set it up for voltage (potentiometer) reading?
Is it really necessary if the device has a speed controller (1-10) ?

Would a speed controller (1-10) be the same thing as a voltage or potentiometer reading control?

I think so but I might need some sleep.

What is the (time) unit in the graph?
One Minute?

(mL./min ???)

 

[Photo Engineer]

All data is collected over 1 minute. The potentiometer is the speed controller. All pumps must have one. I was half asleep when I posted that after doing most of the work and running the plots all day on and off in the DR.

PE

 

[Ray Rogers]

All data is collected over 1 minute. The potentiometer is the speed controller. All pumps must have one. I was half asleep when I posted that after doing most of the work and running the plots all day on and off in the DR.

PE

Perfect,
I was half awake when I read it!

Just curious though, what is the unit of potential(?)
Does it have meaning or is it just a guide, like the numbers on a volume controll knob.

Is this range of possible flow rates typical of the what one encounters in professional work?

 

[Photo Engineer]

The potentiometer setting is a vernier knob on the Masterflex pump that merely connects to a variable pot in the device to alter voltage. It has no bearing or relationship to RPMs or flow rate other than what you physically measure. Flow ranges in professional work range from flows that are barely measurable to flows that cannot be controlled by any pump, and must be physically dumped in for the proper effect. The range over which a given pump and tubing setup works is called its turndown ratio.

If a pump has a turndown ratio of 1:50, then the nominal minimum controlled flow must be 1 (something - RPM, ML, whatever) and the max is 50 of the same unit. A ratio of 50:100 is measured the same way. At Kodak, we keep a stock of various pumps that have different ranges and that measure in either ML/Min or G/Min (volumetric or gravimetric).

PE

 

[dyetransfer]

I once made a very inexpensive DC motor speed controller which used an IC - made by National Semiconductor, IIRC - which measured the back emf (think of the motor as a generator as well as a motor) to sense the speed. Sensing the back emf of the motor provided velocity feedback for closed loop operation. The beauty of this is that it was just one IC and a power transistor, and had very good control of the DC motor speed without using add on devices for sensing rotation speed. I have no idea if NS still makes this IC, but I'm sure something like it still exists. This would give good speed control (within a few percent) over varying loads and power supply voltage fluctuations. A big improvement over a simple regulater power supply and a pot. Regards - Jim Browning

 

[Photo Engineer]

Thinking about this, I believe that I must add some to my previous posts.

Although the pump information I give will work well for all of my emulsions, this is due to design and they are really not modern. If I were to pick a modern design, here are some problems for lab scale work.

at 1000 L and 500 ml/minute flow for 30 minutes, you run 15000 ml or 15 liters into a full scale make.

At our lab scale to make 1 L, we would run 0.5 ml/minute for 30 minutes or 15 ml. This is below the capability of ANY conventional pump and tubing system available, and I cannot hand deliver accurately for 30 minutes.

Here is another problem. Let us say that the flow is ramping up for silver and down for salt #1. At the same time, salt #1 is flowing at a different rate than silver, and salt #2 is ramping up with silver but again at a different rate. This requires 3 pumps. It is impossible with hand delivery and there are no adequate pumps available.

Now, add on the fact that in the middle of this ramp, a metal dopant is turned on and ramped up then shut off. This is now 4 pumps, 4 delivery rates and total confusion if you are doing it by hand.

So, what I am forced to do is re-engineer every single emulsion I know to perform at small scale, on the lab benchtop that any one of you might be using.

Does this help explain more about the design of systems small enough for the home emulsion maker?

PE