Controling just a single lead screw

[damsaddle]

My first automation project. Need all the help I can get. Two objectives here, one, get the job done, but two just as importantly is my learning. Thanks in advance.

Here is a schematic of what I need to do.




Shaft A is turned by another machine.
The speed of Shaft A varies a little during one job. On one job it varies from 0.25rpm to 0.6 rpm.
The speed of shaft A varies a lot between one job and the next. Most jobs are less than 4.0 rpm
There is one job in which shaft A runs at 120 rpm if this complicates this project too much I can build a second machine dedicated to that hiqh speed job.

The Lead screw, B, is the one that I need to control.
I need to control both the speed and the point at which the nut reverses direction.

The speed of lead screw B is a function of the speed of shaft A.
for example:-
job 1- B has to turn at 4 revolutions per 1 rev of shaft A.
job 2- B turns at 225 revolutions per 1 rev of A.
job 3- B turns at 11 revolutions per 1 rev of A.

Fastest that B ever needs to run is 900 rpm the slowest is 1 rpm.

I need to control the point at which the nut on leadscrew B reverses direction as a function of the number of revolutions of A.
eg.
job 1 requires reversing every 49.9 revolutions of A
job 2 reverse at 1.49 revs of A
job 3 reverse direction every 17.85 revs of A
I need a resolution of about 5 degrees of the position of shaft A at which I can set the nut on B to reverse.
Toque required to drive B under load is 0.2Nm max.

Compared to most cnc machinery, it does not need great accuracy. If the reversing of the nut is within 2 or 3 degrees of the angular position of B it would be fine and speed within 2%. Repeatability is more important. There are only 8 or so different jobs and once it is fine tuned, I just keep a record of settings for each job.

I imagine a proccessor controler where I can just set speed eg "4" for 4 revs of B per revolution of A
and 17990 degrees ( 360x50 - 10) of A at which B changes direction. When the jobs are complete the proximity switch is tripped and both A and B stop.

I am quite capable of the mecahanical side of things, have my own lathe etc. so I can easily add gearing, timing belts, pulleys etc. but I am very lacking in my electronics practice.

Questions:-
I assume a stepper motor would be best.
What sort of user interface should I aim for? I've got plenty of old computers lying around that I could dedicate to the job. A computer just seems a bit of overkill to me just for adjusting 2 parameters.


All advice is welcome
Thankyou
dam

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[Jim Dawson]

There are a couple of ways to approach this. One would be to buy a kit from ebay or your favorite vendor

Something like this

Wantai 1Axis Nema34 Stepper Motor 1232oz-in 5.6A 4-Lead& Driver 80V CNC Kit | eBay

and one of these

1 Single Axis CNC Servo Stepper Motor Motion Programmable Controller ST-PMC1 | eBay

Also take a look at the Clearpath servos, you have 3 options here that would work.

https://www.teknic.com/products/clea...-servo-motors/

[KH0UJ]

A raspberrypi + senseHAT module would be best for this project, you can control up to 64 NEMA 34 motors efficiently, program any servo motor at any RPM you want plus if you use senseHAT you can have a direct visual on the mini computer without the need to connect a monitor, you only need 4 LED`s on a single NEMA 34 motor, senseHAT has 192 LED output (RGB) fully programmable in anyway you want, you can even use a USB joystick to directly control the motors manually, like for example mode A first motor turns 4 RPM counter reverse or forward @ 360 degress or @ any rotation you want then switch to mode B which is 225 RPM and vice versa, or you can program it at full auto on all the motors with just a simple python script, every mode of operation needs a separate python script then link all the codes according to your preferences.

[damsaddle]

A raspberrypi + senseHAT module would be best for this project, you can control up to 64 NEMA 34 motors efficiently, program any servo motor at any RPM you want plus if you use senseHAT you can have a direct visual on the mini computer without the need to connect a monitor, you only need 4 LED`s on a single NEMA 34 motor, senseHAT has 192 LED output (RGB) fully programmable in anyway you want, you can even use a USB joystick to directly control the motors manually, like for example mode A first motor turns 4 RPM counter reverse or forward @ 360 degress or @ any rotation you want then switch to mode B which is 225 RPM and vice versa, or you can program it at full auto on all the motors with just a simple python script, every mode of operation needs a separate python script then link all the codes according to your preferences.

Thanks KHOUJ
So I can get input from the shaft encoder from shaft A And the limit switch into the senseHAT and use data as part of programming?

[damsaddle]

Thanks Jim, I've been studying those today.

[KH0UJ]

Thanks KHOUJ
So I can get input from the shaft encoder from shaft A And the limit switch into the senseHAT and use data as part of programming?

Any way you like or want it to do, there`s a spare 4 input switches on the senseHAT built-in joy stick that you can use, if you want more inputs I guess you can utilize the gyro + temperature + humidity sensors wired as inputs so that`s a total of 8 inputs to be used as feedback switch mechanism, outputs no problem there`s a lot you can use 192 outputs to be exact, post your project prototype here I think I can help you with the codes, wiring and everything, saturdays and sundays im free, I also had a raspberrypi 3 and senseHAT just sitting around the corner used as a wireless remote on my project...

[damsaddle]

Ive got my raspberry pi and senseHAT. Ordered stepper, driver and bob a few weeks ago but still waiting on them. Meanwhile playing with the pi.

[damsaddle]

Finaly received my stepper, driver BOB and PSU. Now for a basic question: Do I need to use the BOB? Some info on other forums say not but I will go recomendations here? The driver is a M542t and stepper is 3.0Nm NEMA23. It doesn't bother me if the BOB is spare, this is going to be the first of many projects.
The driver logic signals requires 4-5volts and maximum 16mA. And the driver has optically isolated logic inputs. Can the GPIO pin circuts of the Pi handle that? Do I total the max current for all outputs from Pi's GPIO to check?
Thankyou for your patience, hopefully someone else is getting something out of these basic questions too.

[KH0UJ]

You dont need the break out board, just the raspberry pi and the stepper driver and the NEMA motor, GPIO pins can handle the stepper drivers easily, what it does is only light a LED inside the opto isolator, the speed of the motor will now be dependent on how fast you code the GPIO or senseHAT LED`s, you can now write a code for reverse, and a code for forward, code for high speed and so on and so fourth.

[damsaddle]

Thankyou. hopefully will be wiring it up this weekend. I will have some more very basic questions.

[damsaddle]

This is how I have wired it up. Have not powered it up yet, just want confirmation that this is OK. Not sure about the taking the PUL-, DIR- and EN-to common ground? I think I read somewhere that just to start with as a first step I could leave Enable and DIR's not connected just to see if I could make the motor turn by sending pulses to it. Not sure about that. I want to try very very basic stuff first and keep adding/building up from there. Rather than build something ellaborate at the start and then spend days trying to fix and debug!
I've been experimenting with sending pulses from the GPIO pins to LEDs