Created Date: March 22,2020

Created by: Ken_M

Apologies in advance, I suspect there are terms for what I'm trying to do that I don't know.

I have a conveyor like application, with a sensor and actuator at various points. The conveyor speed varies, but there is an encoder providing total distance traveled information (direction never changes). Id like to store readings of sensors, and the position at which they were read, then have actuators act on a portion of the conveyor when the product that passed the sensor gets to the actuator. Or line up the readings from different sensors from different points so that relationships can be seen.

I'm assuming the first step is to break the conveyor up into minimum discrete lengths. If there were only a few total places on the conveyor, I would get a new reading when the conveyor advances the minimum distance, move reading 9 to 10, 8 to 9, 7 to 8 etc and store the new reading in position one. Then the actuator can act on position 7 (assuming there are 7 distance units between sensor and actuator).

Trouble is, I'm likely to have thousands of positions, so writing this one step at a time seems impractical. Perhaps I can use a MOVER command?

If the values are all integers, what is a reasonable number of values to handle in such a structure? I'd like to update the system 100 times a second, but could probably live with 5-10 times a second

Thanks in advance

Created Date: March 22,2020

Created by: Garry

Hi Ken,

I believe you are looking for a shift register. Here is an example:

https://accautomation.ca/plc-program...hift-register/

This uses Factory IO to show how the shifting works for the conveyor belt, sorting.

Regards,

Garry

Created Date: March 23,2020

Created by: kewakl

I have tried to decipher the memory of the do-more CPUs.

Not sure how to look at it.

Are you sure that the do-more has enough memory to support tracking thousands of datapoints (words???) 100 times per second?

It seems that the (current) domore platform has 1.8MB that can be divided/allocated as you see fit, but you are working toward a lot of data.

{ "alt ": "Click image for larger version Name:\tDomore-Address space.png Views:\t0 Size:\t135.5 KB ID:\t129540 ", "data-align ": "none ", "data-attachmentid ": "129540 ", "data-size ": "full "}

Created Date: March 23,2020

Created by: Tinker

I suppose one important factor is, just what is "thousands "? 2,000 is "thousands " and is much easier to handle than 500,000 (which is also "thousands ") note that by default, the DOMORE allocates 4096 words of V-memory, which is already a fairly significant number and it can be adjusted to be more.

I have no idea how fast MOVER is with a large block, 100 times a second might be difficult, or maybe not.

Created Date: March 23,2020

Created by: franji1

Do-more supports FIFO and LIFO LOAD/UNLOAD instructions. You can have a FIFO of WORDs (easily 5000, 10000, 50000 - even 100000 if you reduce the size of some of the predefined data blocks that you won't be using). What's good is that these are implemented as "circular buffers ", so the data is not "shifted " around, but the "head " and "tail " of the queues are maintained.

You could do it the old-fashioned way with MOVER (where you are constantly shifting the 5000 elements) if that mental model makes more sense.

Circular buffers have 1 level of indirection, but Do-more supports "arrays ".

Not sure what event you would need to FIFOLOAD. How precise? You may want to stick the FIFOLOAD in a timed base ISR to get accurate time events.

Not sure if this is helpful or not.

Created Date: March 23,2020

Created by: Ken_M

Franji1, Can you elaborate how such a task would be done with with fifo/lifo? My first instinct was to use something like that, but I ran into two difficulties (haven't tried yet, just reading the help files). First is that the stack has a limited size (which is fine) and when it fills up, no more can be written to it (which is not, I'd want to loose the end as I keep writing in the front). The second is how do I read a deeper location in the stack? The sensor data is getting written into the stack, so the actuator would need to act on location 5,000 (just as an example). From my reading of the help file, I'd have to unload the previous 5,000 items to read it, loosing them in the process.

Shift registers would work for actuators. They require limiting the stored data to bits (so I can store pass/fail, or bin1/bin2/bin3 if I wanted to write multiple stacks). but that's not good enough for data shifting since I need to store words instead of bits. I can see how to do that with MOVER. Just concerned about about what that will do to scan times. I 've been warned that PLCs don't have the near infinite processing capabilities of computers but have never actually run into this as a physical limitation before.

Created Date: March 24,2020

Created by: franji1

So with FIFO, .Head is the index where the next LOAD will occur, and .Tail is the index where the next UNLOAD will occur. When we FIFOUNLOAD, even though it technically does not matter, we go ahead and clear the memory location at the .Tail. So once we got full, we did a FIFOUNLOAD (from the .Tail), which was at index 1 of the block. So if you look at the Data View, MyData1 is January 1, 1970 at Midnight, which is the 1970 Epoch value for 0 (.Tail should now be 2 after executing the FIFOUNLOAD, since this is the new "oldest " entry). .Head is 1, so MyData1 is where the next FIFOLOAD value will go.

So basically, for FIFOLOAD, the data gets added @ .Head and .Head increments but .Tail stays the same. FIFOUNLOAD will return the value @ .Tail and .Tail increments, but .Head stays the same. The data never moves, the .Head and .Tail point to the "head " and "tail " and are adjusted. This is way faster than MOVER, since scan time is critical. You could have 100,000 entries in your table, and FIFO/LIFO is super fast, just as fast as if it had 100 entries.

Created Date: March 24,2020

Created by: franji1

Franji1: So many thanks, this is extremely helpful!

You 're welcome!

Just to be clear, I can still read any location in the stack, anytime I want, without unloading, anything correct? I just have to do some math to figure out which location I need to read.

Exactly!

You technically could manipulate the values in the queue also, through the same index math. You just cannot manipulate the state of the queue without using the FIFOLOAD/FIFOUNLOAD (i.e. the .Head and .Tail members). There is also a FIFORESET instruction to clear the whole thing (with an option to clear the data values also, but technically that is not necessary).