I have a metal sheet 2mm/30mm/300mm (thickness/height/width). This is conveyed into a guide with an electrically driven roller. I would like the sheet to be flush with the edge.
What is the best way to do this? A stepper motor seems unreliable to me as there could be some slippage. And I can't let the engine hit a stop either because there's no space for it.
Is there a specific sensor that can detect the position of the sheet metal in the guide? Then I could program a control.
I am grateful for further ideas and tips regarding the execution
Thank You
then you could have a sensor "see" the metal sheet coming in and stop the motor. there are many sensory that could work including a mechanical end course detection
another option could be to have a end course detector on a moveable arm that can slide at the end of the guide. when the switch is touched you know the metal sheet is there and you can stop the motor and lift away the end course detector (if needed)
I thought of that too. But the engine has a braking distance and I don't think it would always stop exactly in that position. Then I would have to calculate the braking distance and position the sensor accordingly. Which engine is best suited for this? The sheet has a weight of about 100 grams.
the weight of the sheet matters but it's more the friction of the sheet in your guide that you'll fight against. if you have bearings making the movement smooth then the motor does not need much torque
also you could detect when the metal sheet gets out of the cylinder and get a start time and through calibration define an average time for the sheet to arrive at the end and use that to accelerate and slow down the motor almost to an halt when you approach the end. A stepper would let you do fine grain movement at the very end so that you arrive just where you want.
if you want to be totally flush, may be an extra equipment can rotate and gently push the sheet back in the guide if it did stick out
if the equipment is pretty rigid you could also have a physical limit at the end of the guide so that the sheet can't go further. It will be blocked and you could sense the motor forcing (current increase) and so detect that the bar is at the very end
Hi,
this process reminded me of some machines from my time as a HW technician at IBM.
There were machines that had this need.
The movement of the paper in the printer 1403 and the movement of the read heads of the disks 2319 (231X in general).
The process was like this
If you had to advance 300 positions, you started at normal speed, when you reached 290 you entered at medium speed, and when you reached 298 you entered at low speed, and so you always stopped in the same place.
On modern HDDs, the movement of the HDD heads always stops in the exact spot with micrometer precision.
They use a "voice coil" for the movement and do this process of slowing down.
You can fix a magnet on the plate, and place 3 hall sensors.
One located 10% of the length before the end of the plate and the other 2% of the length of the plate.
And a third at the end.
When detecting each sensor it slows down and when detecting the last one it stops.
I remember that! I ran so many test runs that I could read and look for errors at 1,000 lpm. Also wrote a program to clean the type on a print train. FE cautioned me to NEVER print adjacent characters on a single line! BOOM!
Fond memories. I was the systems programmer, among other things, for a service bureau purchased by an insurance company. Every noon they printed letters on Selectric typewriter print train one one of three 1403 printers. The IBM 360 mod 40 ran three partitions and the ripple print program, on cards, could only run on a non-multiprogramming system. So all jobs had to end before the type train on a printer could be cleaned, as per the document you linked to.
And that is why I wrote the new ripple print program that could be run on BG while F1 and F2 were still making money for the company. Obviously written in good old assembly!
How much force is needed to move the sheet metal blade? If not so much force, I would just put a stop at the end of the guide and let the pinch rollers just slip for a bit when the stop is hit. Run the motor for the maximum time to complete the movement.
If you put a stop at the end of the guide the motor current should increase quickly when the sheet hits the end. So you can
sense the motor current and stop the motor. It should be pretty responsive so that there is no
damage to the sheet
Or position a laser such that when the beam is broke it stops the motor.
For reasons of cost and space, I would like to do without a stopper. There is a possibility and if necessary I will take one, but I would have to take a cylinder that has a very large stroke so that I don't block the way.
That's why I like @ruilviana's idea. I could detect the sheet with a sensor when it has reached 90 percent of the way and then slowly turn the speed back to 0 with a PWM signal so that it comes to a perfectly flush stop. For this I would have to use a DC motor and the PWM signal is already supplied by my PLC.
The second similar possibility is that this time I could use a stepper motor and use a sensor to detect when the sheet metal has reached 90 percent of the way. And then from there slowly move to the correct position with the stepper motor.
I don't know if a stepper motor or a DC motor is better. In terms of price, the stepper motor with motor control is slightly cheaper and has much more torque than the DC motor with motor control. But I don't think I need a lot of torque, I have yet to try that. And the DC motor can offer me a higher speed.
Can you please share your impressions with me again.
Thanks to all
