2 axis control, non-cnc

[kpelley]

Hi, I have an application for a custom prototype machine to simulate a new manufacturing process and I wonder if Centroid has a solution?
There are two axis to control, both in synchronization.
1) Conveyor motor: accelerate from stop, maintain constant speed, then decelerate to stop.
2) Rotary turret: accelerate from stop synchronized with conveyor, vary speed (position) with a programmable cam curve, then decelerate to stop.
This is a rotary liquid dispensing application onto a linear conveyor. The pattern achieved is critical to success, hence the need for a programmable cam-like motion profile.
The motor and torques are not estimated yet; however, I think Nema 23 stepper motors should work. The main reason for reaching out to Centroid is for a two-axis control system with programmable position and speed control.
I have experience with the Centroid acorn product for a CNC router. Thanks for any input. Can anyone recommend a better alternative?

[cnckeith]

Hi, I have an application for a custom prototype machine to simulate a new manufacturing process and I wonder if Centroid has a solution?
There are two axis to control, both in synchronization.
1) Conveyor motor: accelerate from stop, maintain constant speed, then decelerate to stop.
2) Rotary turret: accelerate from stop synchronized with conveyor, vary speed (position) with a programmable cam curve, then decelerate to stop.
This is a rotary liquid dispensing application onto a linear conveyor. The pattern achieved is critical to success, hence the need for a programmable cam-like motion profile.
The motor and torques are not estimated yet; however, I think Nema 23 stepper motors should work. The main reason for reaching out to Centroid is for a two-axis control system with programmable position and speed control.
I have experience with the Centroid acorn product for a CNC router. Thanks for any input. Can anyone recommend a better alternative?
motion profile.JPG

you can make a rotary link to a linear axis in CNC12

so if you issue a gcode with linear and rotary move the linear would be the dominate move in the interpolation and the rotary move would end at the same time as the linear move.

[cncsnw]

A path like what is shown in your graph will need to be programmed as a series of many short G1 moves, because the ratio of conveyor steps to turret steps is constantly changing.

That is okay, because the control should be able to process and run G code lines at a rate of several hundred per second.

You will probably want to write your own software or spreadsheet to generate the codes, but it could probably also be done with variables and arithmetic in the G code program, if you have the formulas nailed down.

Your graph implies very high accel/decel rates at the beginning and end of the move. If you choose an open-loop stepper control, then you will need to beware of dropped steps as a result of exceeding the capacity of the motors or drives.

[kpelley]

Hi, Thanks for your input. I experimented with a 4th rotary axis but got sequential movement. Guess I need to upgrade to Acorn Pro for "4 axis simultaneous movement with full interpolation". Programming a series of short moves and rates sounds doable, I don't think my application is too granular, maybe 20 or 30 moves will cover it. I can graphically calculate the motion and speed in cad. The acceleration rate can be managed by increasing the starting ramp. Sounds like a plan I'll give it a try.

[richardb15]

Usually I'd do something like this with an industrial ladder logic PLC (Siemens, A-B etc) and just develop the equations for a position vs time for axis 1 & 2, then run the PLC on a millisecond timer so you'd get 2000 steps in your example, or do 20kHz or whatever. You can run the STEP outputs to each drive based on a 50/50 duty cycle and vary the frequency dynamically, or run a standard 2.5us pulse and just change the timer that runs between each step dynamically based on said maths equations for the profiles of each axis. By using equations to define the profiles and allowing the PLC to calc in real time the actual position/steps required it saves you having to table it all out or G1 code it into tables. Hope that makes sense.

I guess it depends how often you want to change it, and how un-tamper-proof and windows-proof you want the system, and your budget. A second hand A-B Micrologix 1100 may be $200 and the software is free. You need to know ladder logic and the pain of IP address assignments to take the A-B route though! Certainly not plug and play.

[kpelley]

Richard, I am sure you are spot on with your advice. Unfortunately, I am not a controls engineer and have yet to master ladder logic. I did get the acorn cnc router working thanks to centroid's excellent documentation and support. I am searching for a simple way to control 2 axis. On a past project, I used two SainSmart 1 Axis Stepper controllers ($40 ea.), and started both with one push button to synchronize motion. It worked but I'm sure there is a better way.

[Black Forest]

Have a look at ClearPath servos. I am not sure but they offer some type of programmable logic etc..

https://teknic.com/products/clearpath-b ... vo-motors/

[ShawnM]

Have a look at ClearPath servos. I am not sure but they offer some type of programmable logic etc..

https://teknic.com/products/clearpath-b ... vo-motors/

Agreed, the Clearpath servos have over a dozen operational modes and can probably do what you want and are programmable with their DSP software.

[kpelley]

Thanks, I'll reach out to Teknic.