Suggestion for controlling a Linear Stepper Motor Actuator!

piscis

This is my very first post in this forum. I’m a PLC and VB2005 programmer wanting to learn more about Basic microcontrollers and their programming.
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Right now I have an application which will involve building 30 to 35 custom Syringe Pumping types of machines and need you guys to help me select the correct part numbers and components I will need.
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I need to control a single, frame 23, Linear Stepper Motor Actuator using two Potentiometers.
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1. Potentiometer #1 will Adjust the Stroke from 1” to 8” Inches
2. Potentiometer #2 will Adjust the Speed from 0 to Max speed

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When the operator presses the START button the Actuator will start moving back and forth continuously until the STOP button is pressed.
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Even thought I do not need to make the two adjustments (Stroke and Speed) at the same time I do need to make them while the Actuator is moving.
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I will appreciate receiving the correct part numbers needed to do this project using Parallax’s components. I will like to keep the soldering of components to as little as possible.
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Thanks all
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bennettdan

Do you have more info on the Linear Stepper Motor Actuator?

T Chap

How exactly does a pot control the stroke? I could see a pot controlling the speed in a frequency setting on an op amp circuit, but why a pot to adjust the stroke? To have a precise stroke of a stepper you need to send a precise a mount of pulses to the stepper. Using the Stamp you would send the exact sequence the stepper needs (in parallel) and send them at the right timing to get the speed you want, or, let the Stamp send the Direction and Speed to a proprietary ic like an EDE 1204 or similar. Using an outboard driver you simply use two pins off a Stamp, one is high or low that says which direction to turn, the other is the Step clock pulse that you can adjust the timing of to get the RPM's you need to get to the position. Then, reverse it and go back. It is very straight forward as far as logic. Getting the right stepper driver is another issue altogether depending on the current draw of the motor, the method of moving the actuator (timing belt, ball a screw etc). I see it as the Start button could make it go to 8 inches, Stop goes back to 0. One pot could even set a variable in the Stamp that sets the speed. Without more details it is hard to say. As far as a POT to control the precise distance from 1 to 8, that will be very sketchy. I would use instead something that looks like a pot and could act like a pot called an encoder, that has one pin into it that then distributes the pin to 16 binary possibilities out. I.E. the first detent is 0000, second is 0001 etc all the way to 1111(16ths position). In the Stamp you would program that on Start, it looks at the rotary encoder, goes to the position you assign to it. I am doing the exact same thing with a linear actuator attached to a mic stand in a studio. You dial the "pot" to the desired height, 12 inches divied by 16 increments, then press start. In your case you could make the 8 inches divided over 16 positions, so that each detent on the encoder equates to 1/2 inches.

With Nema 23 you are going to need at least a 2 amp driver off the shelf or custom made. I am designing one now for my own purposes. Making the motor work is no problem, controlling the over current is tricky and taking the most time to get right.

bennettdan

How much prescion does the stroke from 0-8 inchs have to be? You could take the Pot input and Scale it and offset it to output alot of positions from full off to full on.

piscis

http://www.ultramotion.com/products/digit.php

Above is the link to the stepper motor.



The application does not need to be very precise as a matter of fact the only reason we choose a stepper motor is because we thought it could not have been done with this motor:
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Which is really what we want since the cost is much less.
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We thought it was more difficult to implement with this simple DC actuator, perhaps you guys can prove me wrong and convince me to go with the regular 24vdc actuator, still I must achieve these goals;
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Control the Actuator using two Potentiometers.
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1. Potentiometer #1 will Adjust the Stroke from 1” to 8” Inches
2. Potentiometer #2 will Adjust the Speed from 0 to Max speed

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When the operator presses the START button the Actuator will start moving back and forth continuously until the STOP button is pressed.
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Which one will you think easier and cheaper to implement: Stepper or Regular DC motor Actuator and what would it take?
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Thanks all.

bennettdan

If it does not have to be real precise then you can time how long it takes to move then you can use that data and set the stroke by time and rest the data each time the home limit is reached. Using the stepper you can count the steps to achieve the same. I have worked on printing presses that use a time based setup with a syncro motor to move the plates into position. They recalibrate each time the home Limit is hit. This is pretty accurate unless you get a mechanical bind. But I think either should work. Some linier actuators have a feedback also that you can use but I think you can get what you are looking for with a time base setup the adjust the time with the Pot and Speed with the other. How fast of a strok are you looking for time wise? But the code sense you want to change the speed of the stroke counting the steps of the stepper for your 0-8" then it would not matter how long it takes to get their. Is your motor a bi-polar or uni-polar?
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Post Edited (bennettdan) : 6/20/2006 8:54:05 PM GMT

piscis

I need 125 to 175 strokes per minutes. I think I can use the included limit switch on the DC Actuators and reset the timer every time the switch is triggered, this way as you suggested I can change the stroke.

But how do I change the speed?


THANKS ALL for your great suggestion.

Love this forum already!!!

PS. Do anyone knows if Parallax sells complete, assembled microcontrollers with digital and analog I/O's? Or do we always have to do some kind of soldering?

bennettdan

Try out this Stamp PLC http://www.parallax.com/detail.asp?product_id=30064
They also have stepper motor driver cards.

The DC actuators will not travel 0-8" 125-175 strokes if it only moves 60"/min you may have to to use the stepper to travel that fast.

60"/8"=7.5 times a min

Franklin

The stepper he referenced will only do 15"/sec. piscis you will need some mechanical advantage there.

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- Stephen

bennettdan

If you want the 175 strokes a mins at 8" that is almost 24"/sec so you will need a faster actuator or mechanicaly speed it up somehow. What about making your own out of threaded rod and use a DC gearmotor?

piscis

Thanks everyone, as per your suggestion I have decided to go with a custom made actuator driven by an AC parallel shaft, 100 RPM, gear motor. That step motor shown in the photo above was quoted to us at $900, too expensive for our application.

Thanks all again for your great support.

bennettdan

If it is·AC motor how do you plan to vary the speed of the strokes? If you use a DC motor you can build a PWM curcuit to control the motor also the DC motor will have more torque than the AC motor.

Post Edited (bennettdan) : 6/22/2006 5:39:44 PM GMT