Length stop using Arduino, lcd, keypad, stepper and belts?

Projects General Guidance
21

It sounds like a manual lock is acceptable from an operational point of view - but could cause the problem I mentioned.

When I suggested using the stepper to indicate the position for locating a bar manually I was thinking that the motor would move a marker (perhaps flush with the table surface) to the desired position. Then the operator would locate a "stop bar" at that point and lock it in position. That would mean that the belt could move to another position even if the person forgot to unlock the bar.

Maybe you can describe in more detail how the system would actually be used.

Do you need to be able to cut the material to any length from 1 to 9000 mm or are there just a few fixed lengths?

...R

22

Sorry, I forgot to replay You last time about Your suggestion...
No, I would like to try and find an automatic solution. We use this table manually now, we have a tape measure glued on the aluminium L profile, and we slide stop plate to desired length, where we lock it manualy with a screw. Not screwing it exactly, but we have a handle which You rotate with hand a bit, and screw presses against aluminium profile wall this making it locked in position.
We use almost all positions between 1m and 8m, and there are like a thousand usual positions...

23

I think. then, that you must bite the bullet and go for an Arduino controlled locking system even if it does entail a long cable.

...R

24

Not sure if they exist (probably do though), I have seen DC (and AC) motors with brakes on them. If you could find a stepper motor with a brake on it, that could work - the brake releases when the motor is energized then clamps down again when power is removed. Do a Google search for "stepper motor with brake" - this was one that popped up when I looked Did You Know? Holding Brakes on Step Motors | Applied Motion

25

I don't think this problem can be solved with a brake on the motor. The brake or lock must be on the length-stop so that it does not transfer force to the belt or the motor.

I suspect if there were a brake on the motor it would be possible for the belt to rupture.

...R

26

Malium:
Thanks for the replay guys!

The stop plate would actually travel along aluminium "L" profile which serves as a table, so I can make a carriage that would slide along on bearings, closed type that would have no place to move other then move along the length line... It'll be attached to belt on it's ends as it's open loop belt, to create a closed loop. So I think there will be no flex,

However, Robin, You said exactly the same thing I am thinking about for the whole day, and I now do think kicks to a plate will present a big issue, specially with time.
Also, thanks for the thought about manual lock and possible problem if somebody left it locked - I did not think of that, and You are 100% right about that. So manual lock is out of the question.

engineering is the answer.
you could put a lever on the unit and test if the lever is in position.
just like an end switch (which you should have on both ends), the software would test for the lock before moving.
my washer has a test to see if the door is closed before running and my car knows If I am wearing my seat belts.
I used to use a lathe that had a long shaft. each end had a handle and knob. you could put in a full length shaft that locked the stop and then test for lock before doing anything.
on my CNC drilling machine I used a bolt with an arm and a pneumatic cylinder to move the crank arm to lock the part.

27

Robin2:
I don't think this problem can be solved with a brake on the motor. The brake or lock must be on the length-stop so that it does not transfer force to the belt or the motor.

I suspect if there were a brake on the motor it would be possible for the belt to rupture.

...R

I am glad you are taking my comments about locking the stop seriously.

timing belts are rated for length or tension, so the if the belt is selected ( by application for the load ) properly, then the belt would not be a problem. the question is if you want the belt to be selected for the application of also being part of the stop holding, or if you want to only use it for moving. I often comment that application drives selection.

the 'stop to belt clamp' would be key, if it were one screw through the belt, then it would weaken the belt drastically. if it were one clamp over one tooth, it would have a very poor connection. if it had multiple connection points over 50 cm, AND the stop were in a channel to reduce twisting, then the belt wold be enough to hold it in place.
as I mentioned earlier, you could lock the shaft of the motor or the far end. or both.
weak belt clamp = robust locking mechanism.

the manual lock would be easy to test with switches and by far the easiest to implement.
a poor or weak locking mechanism would all for possible failure, and without feedback, such as an encoder on the non-motor shaft as I offered earlier, you would not know there was movement.

but no matter how much you talk about it, some real world testing will be needed.
and there is a good chance that no matter how much you figure-figure-figure some real world phenomena will rear it's head and alterations will need to be made.

here is a VERY poor design, holes in the belt and minimal clamping.

this is much better. since you will have to buy belt material that is open on the end, you need to have a clamp that claps both ends. I would probably add outboard fasteners on either side of the belt as well.

28

I often say that application drives selection.

at this point, I did not find how much force you are putting on the stops. this may be a tempest in a tea cup. as we are talking without knowing the engineering data.

if you are slamming 300 kg sheets of steel on the stop, or 5 meter long pine boards, then the inertia would require a huge mechanical stop.

if you are touching 1cm thick leather belts that are 2 cm wide, then we are not really discussing your application at all.
shame on us for not requesting facts before we tried refining the engineering and component selection.

you can test your force, just take a box, put it on the table, put in a 1kg weight and slam the box. if it moves, put in more weight till it does not. put a string on the box and hang it over table and tie it to a bucket, fill the bucket till the box moves and then weigh the bucket. that would allow for the friction of the box on the table and the weight involved.

thinking about the mechanics, IIRC, your pulley/belt/motor selection is minimal in strength and the belt would probably not be capable of holding with impacts of anything heavy.

29

dave-in-nj:
if you are slamming 300 kg sheets of steel on the stop, or 5 meter long pine boards, then the inertia would require a huge mechanical stop.

That is the sort of problem I have been concerned about.

There must be an economic issue in the choice between a super-strong belt and associated mechanics and a lockable end-stop that allows the use of a "weak" belt etc.

shame on us for not requesting facts

I have requested the facts in Replies #1, #13, #15 and #20

...R

30

Robin2:
That is the sort of problem I have been concerned about.

There must be an economic issue in the choice between a super-strong belt and associated mechanics and a lockable end-stop that allows the use of a "weak" belt etc.
I have requested the facts in Replies #1, #13, #15 and #20

...R

economics and product selection are incompatible.
just what cost considerations do you have when buying a rope when mountain climbing ? would you consider sewing thread because you can get it a $1.00 for a spool?
In my one and only phone conversation with a GATES belt engineer, I found that you can do anything with a timing belt. move a laser scanner, move a CNC milling head, transmission for a tractor trailer or a battle tank. drive a catapult on an aircraft carrier.... the strength in not the issue. the belts can be designed to hold a stop when using those 300kg sheets of steel.
the application drives the selection.
Also, when working on the duPont nylon machine #3, that has been in constant use since about 1935... I came to the understanding that down time of seconds is important when the down time is over $10,000 an hour, or was back in the 1980's
a $300 part such as a timing belt is peanuts when the annual increase in productivity and quality jump to thousands of dollars.
However, engineering also comes into play, why use an L belt when you can use an XL ( or GT2) and remove the forces to a mechanical device such as a stop.
weigh that against a brake on the belt or shaft with fixed wiring vs the cost of cable chain at a cost of $20 a foot to hold the wire on a 6 meter long axis.

31

Robin2:
I have requested the facts in Replies #1, #13, #15 and #20

...R

alas, we still do not know the forces involved.
without that we cannot make any comment on what will work or what will not
for all we know, the forces are like feathers and the electric motor hold is 10 times more force than needed and the GT2 belt will last decades and a motor shaft brake is overkill.

32

dave-in-nj:
economics and product selection are incompatible.
just what cost considerations do you have when buying a rope when mountain climbing ? would you consider sewing thread because you can get it a $1.00 for a spool?

Sorry, but I have to disagree vehemently.

Using a silly example does not prove your point.

...R

33

Hi all,my first post here.
I im just finishing 99% similar project as you are.I am only driving a 3.5meter distance though,but i think 8m is possible.
I am in the step that 80% of mechanical work is done,and about 60% of codding is done.At this point i can drive the stop via the serial input (from pc wherever i want)it remains to put the lcd and keyboard module to be autonomus.About the motor,i ended up using a dc motor with a rotary encoder (from an old dot matrix printer..big motor) wich usinf quadrature encoding provides about 360 signal per revolution.After many..many trials and errors,i ended up reducing the primary gearing (with another small belt-pulley) to 4/1 so i got 4times the resolution and 4times the strength of the motor so it can move easily and precise.Now,i think it could be done just fine with a stepper,but you would need a reasonably big stepper and deffinatetly a gearing down.However you wont have real time lenght monitoring(ican dissable the motor and move the stop by hand..or by a small handwheel on the other side of the belt).
The moving part is a simple,but great construction of square steel pieces,bearings,nuts,washers and threaded rods...it slides great and has no play in any axes,it even has bearings from the botom.
As far as hitting the stop with parts (i am using it to cut aluminum profiles so i have the same proble,) i plan to install a small pneumatic solenoid that will be extended whenever the stop is in position by a small electric air valve.Thats the easy part,that hardest is to callibrate it correctly so you in to 1/2 mm tollerance...An i am there using a dc motor with a rotary encoder.The motor is been driven by an l298n H-bridge module wich is just enough for my motor (about 2ah/25v when moving).
check my first demo here Automatic measure guide for circular saw with arduino and encoder - YouTube
a more ellaborate video is to be uploaded...oh...and its my first arduino project to,i had no knowing of coding etc...it took me about a month until now and lots of hours after work.I am learning fast and its been trully a great experience when you see your effort working...and to something that would impact my work (its for my shop...i make aluminium windows/doors etc) in a very possitive way.

34

Dear Babisgr, great stuff! Many thanks for Your response and insight. I have come to a same conclusions as You did, and I am with pretty much the same level of experience :slight_smile:
I presume You have a real time monitoring with DC motor and encoder? Sound like something I would rather go to than stepper if so. My idea was to code LCD to show step positions, but to try and write a sketch that would calculate and output mm values absed on step to mm equation. So in fact, I would fake feedback. It would not be real feedback, but if result would be precise, should work. I do not know in this point in time if this even possible, but that's an idea I had in my head if I went with stepper. Still deciding on the motor...
I could have some questions for You in some stage, if You would not mind?

Dave and R, sorry, my intentions were not to withold any information, english is not my language and I try to write as little as possible to avoid confusions and mess.

I thought a lot about a problem with locking a length stop, and I thought about simple worm gear. How do You guys feel about that?

The force that will kick in a stop plate is not very heavy, I can only assume as there is hand pushing the material involved, but material is flexible and the force applied to a stop will not be linear, it will brake in another direction after hitting the stop. Also, the stop plate will be on a carriage that has no play in any other direction than in itended one, so I think we speak about 10 - 15 kg of kick to a plate for a fraction of a moment.

If my reasoning is correct, worm gear will alow motor to rotate the belt when positioning, but it will not allow stepper shaft to move when kick to a plate happens. So this should solve this issue on a motor shaft - worm gear will drive the pulley.

Then there is a belt flexibility, if it will move and stretch in case of a hit resulting in stop plate to move some distance despite the motor being locked. Think I could maybe solve this on a plate itself, via allowing plate to move, but on a tensioned spring mechanism that would kick it back in place right after the hit. It should absorb the hit, and I could create an adjustable tension to fine tune it when in place and after some tests. Material I push and which hits the plate is flexible up to some point, so it should work, in my head at least. :slight_smile:

Also, I think Nema 23 is an optimum sized motor in regards to keeping the project under reasonable investment, as in this moment I really cannot tell if there will be a sucess or all components will be thrown in a box after.
I know I may have went a little light on components, but in my head, it's easier for me to create a solid motor stand and fixate a shaft on the open side as well, and do the same thing for the pulleys, make them stronger mechanically. Belt is 9mm wide, it's the only one I could find in 20m length that would not cost me a kidney. 20 teeth pulley should give me a good precision and keep torque request low, as Nema 23 will let me start with 24V power supply. As stop plate will be driven on bearings, I think there is no need to go higher in motor strength. And as I said, I consider this as a proof of concept, not a heavy duty industrial solution.

Dave, my idea of belt installation and usage is exactly like in Your second picture, I have ordered exactly the same belt plates, and the metal chunk where plate is screwed into, would in this example be my carriage on bearings with a aluminium plate on one end, that would act as a "stop".

35

Shoot any questions you might have...i would be glad to help if i can.
About the stepper,it should work,but...you might need a gearing for the primary drive,it would stress the stepper a lot,and they tend to heat ALOT since they always draw power...even at rest.
Yes i have real time length monitoring,and becouse the cloesed loop the system runs,even if you force stop the motor,or push out it will always go in the target position when its free.From a search i have done in similar industrial machines (i was planning to get one..) they use encoders and dc motors and pneumatic cylynder for stop.Some use pulleys and belts,some racks and pinion.
For low cost motor,get a car windshield wiper motor and use it in combination with a high resolutiuon encoder.That motors have great torque,2 speeds and use worm gearing so it would lock itself when stopped.(I used the printer motor cause it had the encoder on it already,although i got a windshield motor to use..10euros used).
For the 2 shafts i used 4 pillow block upc bearings with 12mm inner diameter for 12mm steel shafts.
The belt similar with yours...9something mm and the pulleys are 2x 30teeth (if i am correct) and for the motor gearing is 15 at the motor and 60 at the axle.

36

I like the idea of going to a servo.
there are more than a few threads on how to use a servo.

as for the belt, you can use a chain, like a bicycle chain. if you find you need more strength.

no matter what you use, there will be flexing when there is impact.
you goal is to allow and compensate, or add strength.

37

ok..so to whom is interested a new updated video here..