[Bread_O]

Heres a little brain Teaser for all you electronics gurus out there.

I want to build a automated guilotine that can do this:

There are two blades on seperate ball screws in a straight line. Home would be the centre where the two blades meet. If you wind the one ballscrew to clockwise and the other anti-clockwise then the two blades would move away from each other. It is very important that the two blades move equally away from the home position.

I want to build a controller that can do this but simply entering a measurement in and the blades must move.

I would assume a keypad and small screen is need as well.


Anyone know of such a controller??? or can give me any advise?

[Al_The_Man]

There are a few options I can think of and it depends on the level of sophistication and budget you have.
For instance, do you want the blades to move at exactly the same rate and/or just arrive at the destination at exactly the same time? Or just arrive at the equal position, but not necessarily at the same time?
Usually in the CNC/control world, Stand Alone means the system does not rely on any other operating system to load first, as in a PC based system.
This then would possibly mean a Stand-alone 2 axis motion card system, like a Galil 1500 & Maple Sytems Operator Interface, a PLC (programmable Logic Controller) system with OP interface, or a PIC MicroController based system, the last of which is possibly the cheapest , but requires the most engineering.
Also, if you want to go with steppers, they would be the cheaper, but servo with encoders will give you position confirmation.
Al.

[Bread_O]

Thanks Al,

It doesn't matter if it moves at the same time or not just must move the equal distance from the centre.

Example: If i key in 20mm in the key pad then both blades must move 10mm from the centre.

Cheapest way for now but I also need accuracy.

[Bread_O]

A simple control like this would look silly to have a computer to control it so thats why i opt for a stand alone controller

[Al_The_Man]

A simple control like this would look silly to have a computer to control it so thats why i opt for a stand alone controller

Actually that may turn out to be the easyiest/cheapest if you used steppers with a PC and Mach s/w.

The as-cheap alternative for a true stand alone like I mentioned is ebay for a Galil 1500 & Maple Display.
It depends on the level of expertise you already have and as to how much pre-engineering you need.
I know of nothing off-the-shelf that you can pick up an run with.
I have implemented similar projects using some HMI software that will run with the legacy Galil DMC-600's DMC-1000's, these sit in a PC slot, but ISA PC's can be picked up for next to nothing.
Al.

[Bread_O]

What about a controller with a up and down buttons?

Up would increase the distance between the blades and down would decrease the distance.

This is more manual I know but would be cheaper ???

As long as one motor turns clockwise and the other anti-clockwise the same ammount

Any ideas?

[vger]

As long as one motor turns clockwise and the other anti-clockwise the same ammount

Any ideas?

Yeah, just wire both motors to the same output... but swap phase windings on one so it turns backward.

[Bread_O]

What motors can I use?

Just needs to turn the ball screws

[epineh]

What about simply linking the two screws ? If they always have to be the same distance from centre then a simple pulley system or mechanical drive to suit would achieve this, leaving only one motor required, if all that is needed is simple input from a keypad then I would choose a microcontroller, PICAxe is supposed to be very simple to program, never used one myself though.

Just depends on how complex of a control you can build, and how much time you want to spend on researching Microcontroller programming.

Good Luck!

Russell.

[Bread_O]

If I link the shaft then one needs to have a left hand tread and one a right hand tread. I do not have the facilities to make this sort of shaft. But normal ball screws are off the shelf. I like to make it a bit user friendly for the operator because the distances will change frequently depending on the order we have.

Where can I get these type of microcontrollers. I have no experience with electronic but have a good knowledge of computers, Basic programming and machine building.

Any advise will be appreciated

[Al_The_Man]

Check the MicroChip site, they have application notes and sample programs etc.
Al.

[Ron22]

You could try a Delta Tau PMAC card. They have the capability to run standalone. You can program it through a com port. Or plug it in to your computer. You could then use some BCD Switches to set the distance and a start button to make it move.
I see PMAC Lite's go on ebay cheap.

[keebler303]

If you don't need the advantages of ballscrews, you can buy an acme screw premade with left and right hand threads.

http://www.nookind.com/acme/AcmeTwinlead.cfm

On the controller, I would recommend a PIC. I have just recently gotten into programming them and I have written a program which will move a stepper a set amount for each button push. It could be modified slightly to work in your application with an up/down button type deal which would move (1mm for instance) each time the button is pressed. A simple led readout could also be attached without too much difficulty.

Shoot me a PM if you're interested in the program.

Matt

[vger]

If I link the shaft then one needs to have a left hand tread and one a right hand tread.

Some small bevel gear sets will accomplish this, much like the diferential in a car. Elevate the rear of the car, hold the drive shaft tight, turn one rear wheel and the other turns the oppisite direction.

Would acme thread provide the required accuracy ? If so, acme is available in right and left thread and could be directly linked. I've seen assemblies that perform a function similar to what you are describing that use a loop of timing belt or a chain with knife carriers attached to either side of the loop.

Suppose you took 2 parallel rods with the knife carriers on both rods with bushings or linear bearings, ball screw down the middle with a nut on one carrier only and a hole in the other carrier larger than the ball screw. Then a loop of steel band (similar to the early floppy drive head actuators) with one side of the loop attached to the driven knife carrier and the other side of the loop attached to the other carrier. The loop ends could be put around bearings. Just a thought.

Steve