Acorn single axis

[kwmo]

Hi All,

I have a spindle moulder (think large router in a table) that currently has power up/down on it's Z axis which is the only axis it has. I'm thinking of adding positioning capability by changing to a servo motor for up/down and adding a linear scale for positioning. This is only used for setup, not while machine is in cutting operation. I have an acorn board that I bought quite a while back and was thinking of using it vs doing a PLC w/motion control and having to re-invent the wheel of virtual MPG, etc on the PLC HMI. I thought I would ask the experts here a few questions about what's possible with the acorn since this isn't the usual use case. I know the wizard doesn't support much/any of this but can the machine parameters be set to allow:

1) position correction with the linear scale if I have the appropriate CNC12 license?
2) turn off all axis but Z

Basically this would just be used during setup of the cutter and the only g-code programs it would ever run would be to restore a Z axis position for a particular job.

Thanks,

Kevin

[carboncymbal]

Hey Kevin, I don’t see any reason why this wouldn’t work, although it seems like there won’t be much savings. It will require a Computer, screen, driver, motor, linear scale, and all of the supporting electrical equipment(including any needed safety equipment).

Personally, I would take a different approach. First, is the linear scale really required or can it be met with accurate motor positioning? If it’s required I would consider this approach.

Consider the delta ASDA-A3 servo motor drivers (or Automation Direct sure servo 2). If you have a few limited positions, you can this with switches. Others wise you could use an HMI to interface with the servo drive (I think they can interface directly, otherwise you may need to put a small Click PLC in the loop). Something similar can also be done with the right clearpath servo.

How many positions would you need? What level of positioning accuracy do you need? What is the total travel distance?

Depending on these answers. You may be able to use even simpler solutions.

[kwmo]

Thanks for the reply. Positions are infinite based on cutter, material thickness, and desired profile you are trying to make. Right now with calipers, digital height gauge, and setup blocks I'm able to manually position within .001 (just takes a lot of time) so I would want to keep the same accuracy. I believe it would require a scale to get to that accuracy since the machine does not have a ballscrew and has some backlash. The total travel distance is ~6.5". I already have the acorn, pc gear, and several DMM DYN4 servos along with all the supporting gear in my hoard of machine gear so the PLC would actually be an expense. I know the acorn is overkill but just trying to use stuff I already had if it would work. I played around with it today and was able to disable all axis except Z. When I try to enable the scale for the axis I get a message about the feature not being unlocked so I'm guessing it requires a pro/ultimate version - maybe someone from Centroid can chime in on that or I may have to give them a call to see.

[carboncymbal]

That makes sense. I imagine someone will point you in the right direction on the scale.

I wonder if you could address the backlash issue with backlash compensation or by using standard positioning moves where you always approach the desired position from the same direction.

Finally, if the moves are infrequent (say, a few an hour or less), you might look at adding a cheap dro scale and using a paper list with manual adjustments. If I were managing the operation (if in a production environment), I’d be concerned about the added complexity of the machine.

[kwmo]

The digital height gauge is essentially acting as a DRO and is how we are doing it now. The machine has a hand wheel for manual adjustments but with the current induction motor and rocker switch the power up/down is obviously not very controllable and it just takes a long time to dial in and/or repeat. After thinking about it even if the scale doesn't work for position correction on acorn I could always just use the dro display and just jog and/or hand wheel to get exactly where it needs to go. How does the axis DRO display when position correction is not being done? Does it just show the scale value or does it show where it thinks the axis is?

I'm not too concerned about the complexity since worst case I could just use the hand wheels. I'm really on the fence vs using a PLC. The PLC would easily do what I want and could be programmed to do specific things a shaper does but I would have to do an HMI if I wanted the fancy DRO display, etc.

[suntravel]

Even single axis Acorn is full CNC. If the axis is konfigured ok, you can set Z 0 for the lowest point and use MDI with G1 Z0.5 F200 to drive exactly 0.5 above the lowest point.

Since Acorn is with one encoder port ist is possible to connect a scale. I am only not sure if ultimate is required for closed loop.

Uwe

[tblough]

I don't see why you would need micron precision for a shaper, and therefore why you would need scale feedback. Up/down control is no different than any other axis with Acorn, and once revs/in is correctly calibrated, you will have your DRO position with plenty of accuracy.