Measuring distance travelled on an axis of a large paper cutting machine

Hello,

I am a total beginner in regards to Arduino and its various components, and I’d appreciate your insight and experience on this.

We have an old paper cutting machine, for very large sheets of paper (that can measure up to 1 meter in length). The machine being old, it doesn’t have any of the automations that the newer, more expensive machines have. You have to measure each single cut with a ruler before actually cutting the paper.

As you can imagine, this can get very tedious very quickly. To get a glimpse on the workflow, you can check this sort video:

Bear in mind, this is a new, fully automatic machine, so the operator enters the desired dimension, the machine moves its single axis back or forth to the desired location, and then cuts the paper.

In my older machine, you have a hand crank that is connected to a lead screw that drives the thing that you see in the picture attached. This thing in turn pushes the paper to the desired location in order for it to be cut.

Adding a vernier scale is impossible, as far as I am concerned, as it would need to be almost 1 meter in length.

I was thinking of adding an absolute rotary encoder directly to the acme screw, which would count the revolutions. Knowing the pitch of the screw, the Arduino would then make a simple calculation and then show how far the thing in the back of the machine is from the 0 point (aka from the point where the cutting blade depresses).

My main concerns are:

  1. This needs to be very very accurate. Within 0.1mm or better.
  2. Will it need a homing switch?
  3. How can I account for backlash and for anything else that might skew the final results?

Thank you.

photo with explanation.jpg

Have you considered buying a digital readout linear scale?

...R

Robin2:
Have you considered buying a digital readout linear scale?

...R

I didn't know about these until now, and I have to say that it's a great idea.

I have found a linear encoder with a 0.005mm resolution, which uses TTL and a 9 pin DB-9 connector. The pinout reads as follows (from the item's description):

Pin 2 Black 0V
Pin 6 Green A
Pin 7 Red 5V
Pin 8 White B
Pin 9 Orange Z

From my very limited knowledge, I came up with this: use a TTL to serial adapter board like this one:

and then hook it up an Arduino with an LCD for digital readout? Are there any compatibility issues that I am not aware of?

orestes_:
I didn't know about these until now, and I have to say that it's a great idea.

I have found a linear encoder with a 0.005mm resolution, which uses TTL and a 9 pin DB-9 connector. The pinout reads as follows (from the item's description):

Why not just get one that has its own display?

...R

Robin2:
Why not just get one that has its own display?

...R

I've only found one that can travel up to 1000mm and it's accuracy is within 0.2mm, and is more expensive than the 1000mm 0.005mm accuracy one that doesn't have its own display. If you have to double check the measurements with a ruler it kinda makes this whole system redundant.

The 9 pin dsub connector that it has actually utilizes just 4 of the pins (GND, VCC, V1, V2) and from these two videos:

I only have to figure out which cable is which in that specific linear encoder, then do the wiring and the coding. However, there is one glaring issue with this: If you move it at anything faster than a snail's pace, the Arduino can't cope with all the input in time, which in turn causes missed steps.

I was wondering if something like this, including overcoming the missed steps problem, is possible for an Arduino beginner like myself, provided that I am willing to put all the effort into making this happen.

Before you go too far in your project design, consider you absolutely have to design in a zero point in your system. Accuracy is not worth much if you don't the exact same beginning point each time you use your system.

Paul

Paul_KD7HB:
Before you go too far in your project design, consider you absolutely have to design in a zero point in your system. Accuracy is not worth much if you don't the exact same beginning point each time you use your system.

Paul

Forgetting the off the shelf solution, which has a button to zero out the measurement, wouldn't a simple end stop switch suffice?

orestes_:
Forgetting the off the shelf solution, which has a button to zero out the measurement, wouldn't a simple end stop switch suffice?

Not for the accuracy you are designing for.

Paul

Paul_KD7HB:
Not for the accuracy you are designing for.

Paul

So basically the only way forward is going with this? From what you've told me so far going with the diy solution could end up costing more and yielding sub par results.

orestes_:
I've only found one that can travel up to 1000mm and it's accuracy is within 0.2mm, and is more expensive than the 1000mm 0.005mm accuracy one that doesn't have its own display. If you have to double check the measurements with a ruler it kinda makes this whole system redundant.

Digital Readouts are very common on machine tools. I would be very surprised if you can't get one a metre long or much longer with its own display.

If this is for a business then it is not the time for penny-pinching and amateur DIY solutions. Who would know how to repair the DIY solution if it goes wrong? It would be very unwise for a business to rely on a single person who might get ill, be on holidays or leave the business.

...R

orestes_:
So basically the only way forward is going with this? From what you've told me so far going with the diy solution could end up costing more and yielding sub par results.

shahe new 1000 mm 0.01 mm Magnetic Remote Digital Readout digital linear scale External Display|Level Measuring Instruments| - AliExpress

Even with that device, you need to manually zero it then the paper movement is also at zero.

Paul