Sorry for the long post. Pallet machine.

Hello, I am new to the forum although I read them a long time ago.
I will be honest, it is the 1st time that I am going to build something of this size and I have many doubts. I am an electronics technician and programmer, so my problems are in mechanical design.

I want to automate a certain stage in the manufacture of wooden pallets.

https://i.ibb.co/CstRN7p/IMAGEN-1.png

The distance between guides is 950mm and the length of the screw is 2000mm.


For this, I have an X axis that must move 3 pneumatic nail guns with its own Y axis with an approximate weight of 125lbs (57Kg).
The total travel of the X axis is 1215mm, having to stop at certain points to apply nails:

https://i.ibb.co/3SJR1Dy/IMAGEN-2.png


- From a rest position it moves 130mm and stops to insert the 1st nail
- Then it shifts 25mm, and inserts a 2nd nail
- Then it shifts 505mm, and inserts a 3rd nail
- Then it shifts 25mm, and inserts a 4th nail
- Then it shifts 505mm, and inserts a 5th nail
- Then it shifts 25mm, and inserts a 6th nail
- Finally it returns to the rest position traveling 1215mm.

I have read and searched in this forum and in google, but the classic examples and uses are usually "slow" machines, machines where the speed of the task is not important. In my case, I need it to be done in the shortest possible time, around 11 seconds at least.




Before going to the calculations, these are the pieces that I plan to use, but I'm not sure if I have sized correctly:

https://i.ibb.co/5k7Z3qw/IMAGEN-3.png


- Linear guides: HSR25 + HSR25CA

https://www.amazon.co.jp/TEN-HIGH-%E...al&sr=1-6&th=1

- BallScrew: SFE4040

https://www.amazon.co.jp/dp/B07LG7BB...08&sr=8-4&th=1


To calculate the torque and rpm of the servomotor I used these equations:

distance to travel = 1215mm
estimated time = 2.5sec
lead screew = 40mm

laps needed = distance / lead screew = 1215mm / 40mm = 30 laps
rps = (laps / time) = (30 laps / 2.5 sec) = 12rps
rpm = rps * 60 = 720rpm


I want to use a servomotor from the Teknic catalog, I took for example the following:
https://www.teknic.com/model-info/CP...del_voltage=75

Peak Torque: 1,383 oz-in (9.8 N-m)
Cont. (RMS) Torque: 323 oz-in (2.3 N-m)
Max Speed: 1770 RPM



Here my doubts begin, be patient with me please:


To calculate the torque I followed this video:

https://www.youtube.com/watch?v=xqrb...youtu.be&t=132


Inertia= Motor inertia + Screw inertia + Carriage inertia

-Motor inertia: 15.5 oz-in² (2.8 kg-cm²) value taken from manufacturer
-Screw inertial: I have not found such value, I assumed twice the value of the video, just to put a number = 0.002 oz-in-s²
-Carriage inertia: payload mass * load mass factor (not having the load mass factor, I assumed twice the example in the video)


So: carriage inertia = 125lbs / 386.4in-s² * 0.002 = 0.00064699 lb-in-s²




Now, with the sum of the inertias, I calculate the torque:

Torque = Inertia * Acceleration = (15.5 oz-in² + 0.002 oz-in-s² + 0.00064699 lb-in-s²) * (30 turns / 2.5sec)

I convert the drives to the same system first, using this page: https://www.magtrol.com/inertia-calculators/


Now:

Torque = Inertia * Acceleration = (0.04015 oz-in-s² + 0.002 oz-in-s² + 0.01035 oz-in-s²) * (12 rps / 2.5sec) = 0.25215 oz-in-rev => 0.25215 oz-in-rev * 2 * pi = 1.584 oz-in = 0.01 N-m




Are these calculations correct?
I feel that the final value is very low, even multiplying it by 10!

If I choose a smaller motor, its inertia coefficient also lowers, so again there is excess power? I am really lost here.


Also, could you choose smaller linear guides and BallScrew? for example:

- SFE2525: https://www.amazon.co.jp/dp/B07LG6CG...75&sr=8-2&th=1

- HSR15 + HSR15CA: https://www.amazon.co.jp/TEN-HIGH-%E...al&sr=1-6&th=1


I am currently in Japan. Due to the coronavirus, I cannot return to my country and this project arose, but I do not know the country as well, so I do not know where to buy these materials except for Amazon.

I would like to be able to make more specific queries, I apologize for the extensive post.
I will be very grateful to you with any help to choose the parts and to be able to calculate the motor to choose.

I will also appreciate your opinions when choosing. I would just like to keep the brand of the servo motors, simply because I like the option they offer to be able to have a graphical analysis of the motor response in real time. This will help me get a feel for what those numbers look like in the real world. That really would have helped me right now!

It's always difficult to figure out if you're being trolled or not by someone with one post. LOL. Don't take that personally.

What kind of a budget do you have for this?

I don't have time right now to go through all of this and fix it, but no, your math and assumptions are not correct.

For this kind of machine, you don't need a ballscrew. Look for a surplus belt driven linear stage (or two) for your long axis. The linear rails are built in. Easy button.

The 3 air nailers....do they only move up and down? What is the point of your Y axis? Does each air nailer move independently on the Y axis, or do they all move together?

For math, I'd start with this....using basic acceleration, distance, and time equations, figure out the top linear speed you would need to achieve for linear accelerations of 0.25G, 0.5G, 0.75G, 1G, 1.25G, 1.5G in order to complete all of the movements on your X axis within the amount of time that you need. Make a table in Excel. 1G is 9.81 meters / second^2. Metric, metric, metric :).

From that you will be able to pick targets for linear speed and acceleration to start with.

Hi Gabriel - I agree with Nik. For this application belts are the go. They are light and fast and will not suffer whirling or whip like a 2m screw will. If you can't find a stage the separate parts are easy to get to build your belt drive.

For future reference in an inertia calculation you separate the linear inertias and the rotational inertias. If you go to the Hiwin site they publish all the equations you may need. You may have to balance the gun axis against gravity to improve its performance.

Linear guides are sized by static weight conditions and the required life (dynamic or fatigue conditions ). If you look at the Hiwin rail design manual you will be able to figure out the static and dynamic conditions and then decide if the rail is too small. But as Nik says get the bigger picture of cycle times and motion better defined before you move forward so to speak..

The reason to use a servo is more speeeeeed or more torque then a stepper can provide. In this application I expect its cost sensitive unless you can justify the much more cost servos will be by extra speed. So once you figure your torque requirements you may find steppers do the job easily which saves $$$ which usually makes the boss happy.... Cheers Peter

Since the nail spacing does not change or changes infrequently you may find that having 3 sets of 3 guns is cheaper and better then having the gun axis move. It will be clearly faster if the guns only move up and down. The guns & frame I expect will be relatively cheap. Then you could do the machine with a pneumatic up/down system vs the more complex CNC one proposed.

You have each gun on an independent axis. This is a lot of repeat $$$ and complexity. You could make a frame and move all the guns on the same axis unless you need independent control of each gun, which I'm guessing you don't. So you could move 9 guns all at once to achieve your result...I would even consider leaving the guns stationary and raising/lowering the pallet to the guns on a platform seems easier to me. cheers Peter

Quote:

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Originally Posted by NIC 77

It's always difficult to figure out if you're being trolled or not by someone with one post. LOL. Don't take that personally.

What kind of a budget do you have for this?

I don't have time right now to go through all of this and fix it, but no, your math and assumptions are not correct.

For this kind of machine, you don't need a ballscrew. Look for a surplus belt driven linear stage (or two) for your long axis. The linear rails are built in. Easy button.

The 3 air nailers....do they only move up and down? What is the point of your Y axis? Does each air nailer move independently on the Y axis, or do they all move together?

For math, I'd start with this....using basic acceleration, distance, and time equations, figure out the top linear speed you would need to achieve for linear accelerations of 0.25G, 0.5G, 0.75G, 1G, 1.25G, 1.5G in order to complete all of the movements on your X axis within the amount of time that you need. Make a table in Excel. 1G is 9.81 meters / second^2. Metric, metric, metric :).

From that you will be able to pick targets for linear speed and acceleration to start with.

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Hi Nic, trolling?! o_o I guess my idea was really wrong, right? no answer needed haha
Thanks for the little slap: after reading about belts I imagine your horror face when seeing my proposal with ballscrew xD

Budget? about $ 4000 dollars. But he is flexible like my boss's sanity and humor.

Quote:

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Originally Posted by peteeng

Hi Gabriel - I agree with Nik. For this application belts are the go. They are light and fast and will not suffer whirling or whip like a 2m screw will. If you can't find a stage the separate parts are easy to get to build your belt drive.

For future reference in an inertia calculation you separate the linear inertias and the rotational inertias. If you go to the Hiwin site they publish all the equations you may need. You may have to balance the gun axis against gravity to improve its performance.

Linear guides are sized by static weight conditions and the required life (dynamic or fatigue conditions ). If you look at the Hiwin rail design manual you will be able to figure out the static and dynamic conditions and then decide if the rail is too small. But as Nik says get the bigger picture of cycle times and motion better defined before you move forward so to speak..

The reason to use a servo is more speeeeeed or more torque then a stepper can provide. In this application I expect its cost sensitive unless you can justify the much more cost servos will be by extra speed. So once you figure your torque requirements you may find steppers do the job easily which saves $$$ which usually makes the boss happy.... Cheers Peter

Since the nail spacing does not change or changes infrequently you may find that having 3 sets of 3 guns is cheaper and better then having the gun axis move. It will be clearly faster if the guns only move up and down. The guns & frame I expect will be relatively cheap. Then you could do the machine with a pneumatic up/down system vs the more complex CNC one proposed.

You have each gun on an independent axis. This is a lot of repeat $$$ and complexity. You could make a frame and move all the guns on the same axis unless you need independent control of each gun, which I'm guessing you don't. So you could move 9 guns all at once to achieve your result...I would even consider leaving the guns stationary and raising/lowering the pallet to the guns on a platform seems easier to me. cheers Peter

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Peteeng, i checked the Hiwin site ... too many equations, it will take a while but clearly been very helpful, I even found a similar guide in Spanish (my native language).



The Y axis is necessary because they are actually 3 nails (forming a triangle), in each joint of woods, and cannot simply be in line:

https://i.ibb.co/jbFWDfZ/Captura-de-...s-11-11-22.png

All 3 pistols can be activated at the same time. Actually, I still haven't thought about how to make the Z axis. Due to the weight of the guns, I imagine that I must take into account that there will be a tendency to fall when I don't energize the motors. But I know that there is information in the forum for those questions, although a tip is always welcome ;)
I discarded the idea of ??using pneumatic actuators because I need to nail a board onto a cube, and then another board, so there are 2 positions (not counting the rest state) on the Z axis.

The first 3 nails are not aligned with respect to the following 3 nails that are on the next wood, they will collide:

https://i.ibb.co/2hQ9wM9/Captura-de-...s-11-37-55.png
https://i.ibb.co/mTM6KYY/Captura-de-...s-11-37-36.png




When I have a new model I will share it, although I think I will have to put many led lights to improve its 1st impression, hahaha.

Thank you very much for your help!!!

Hi Gabriel - Well this tells me that you should consider only one gun for the Z axis. The manual loading/unloading and turning over of the pallet will be the slowest operation. The nailing will be much faster than this even with a single gun. So You will have a two station machine. One side the operator will be loading while the other side is being nailed. The operator can simply push the frame to a detent and the machine will be interlocked so it knows which side its on (or you make a long machine maybe better, the only cost is extra drive which is not much cost). Once the operator flips the pallet they push a B button and the machine comes back and nails the B side. The operator then goes to the other side and unloads or flips, hits the A button and the machine comes back and nails the A side etc. If you do a time and motion study and figure out Takt times you may find a 3 or 4 station is the go to balance machine time and manual time...I used to design and program robotic workstations and its always a juggle to balance labour vs machine time so the operator is busy but not uncomfortable or has too much free time....Peter

You could use a ballscrew on your long axis....but 40mm diameter is a bad choice....especially for a machine like this. The extra rotational inerta on such a large diameter ballscrewscrew, there's no point to it. You would be way better with something like a 2540 ballscrew.

Since you want fast speed, and the application is air nailing, and you have a long axis (which you might even decide to make longer), belt drives are a good option.

Check out these links

https://www.ebay.ca/itm/New-Festo-To.../274040744321?

https://www.ebay.ca/itm/Festo-DGE-Se.../133014327867?

That's the kind of stuff I'm talking about. If you can find it surplus.

I agree with peter that a two station machine would make this more productive. Perhaps you can't manage this at the moment, but at least you need some extra movement at the end to "park" the gantry to the side so that the operator can load / unload clear of the gantry. The load / unload will dominate the time factor.

Obviously, some kind of safety lockout so the operator can't accidentally get hurt is also necessary.

I don't see a problem with moving all of the air nailers back and forth at the same time.

https://www.youtube.com/watch?v=GPzIsIyyJSk

I like how this machine is angled, I'm guessing this makes the load / unload much easier. Belt drive driven.

For a machine like the one in the video, IMO, belt drives, rack and pinion, or even a chain drive are pretty much the only reasonable options, on the long axis.

You mentioned a budget of $4K in total for the project. I don't see that happening. You're going to be over. You might want to re-evaluate a breakdown of all the costs, including wages, to start with.

I've been thinking about this some more.

A 4'x10' or 5'x10' Avid Pro CNC (cncrouterparts.com) with 2 extra Z axis could be easily modified into an air nailer for making skids. 10 feet should be able to let you have 2 cells based on your current measurements. I'd ask them if they can do 12, or if 10 is the max.

With the rack and pinion, you could also have each air nailer be able to move independently, but this would require an extra 2 axis of motors for 8 in total, plus you'd have to home them all, so extra limit switches too.

For all 3 air nailers moving in unison, but independent Z axis, 3 Nema 34s and 3 Nema 23s, and you could probably mount the T-Slot on an angle, like the one in the previous video I posted. That would give 6 axis of movement, which could be handled by Mach 4 or UCCNC. Actually, 2 of those motors would be driving the same axis, but it would be nice if each one could be homed independently to prevent gantry skew. One thing I'd ask about. I think they might have 3 on the X, 2 on Y, and one on Z, if so it should do it. You'd want an extra 2 for Z, I think, with the 2 extra Z axis.

T-slot is easily modified and you could ask for pieces (like the gantry offsets for example) to be a different length to suit your needs. Not sure if they would be willing to wire up a 6 axis controller for you, but I bet they would.

I'm guessing the cost when all is settled would be about 15-20K for that.

6500 for the kit
1200 for extra Z axis
3000 for the electronics box & motors (assuming they'll put together a 6 axis one, they only advertise 5)
250 proximity switch kit ask about the extra axis you may need a couple more, I don't know what the board can support?
???? Air Nailers and Pneumatic lines
1000 (guess) for extra aluminum t- slot to hold the table at an angle
500 (guess) for materials to make jigs to hold your boards in place
Shipping and tax on top.....

If it's for a business and you just want it to be up and running soon without all the hassle....that's one way to do it. You could start by figuring out how much money you loose per month by not having it?

They claim it will do 1100 IPM, but I don't know at what acceleration.

Probably still less expensive than buying the machine in the video in my previous post....does anyone know what those cost?

I think the industrial belt drive is a better option as far as what you might get at the end of the day, for your specific application. But that's only if the person who is designing it and building it executes it perfectly, and you can find enough superior quality surplus parts.

https://www.youtube.com/watch?v=kBR2uZhRZrs

Hi Gabriel - Turning the pallet over is going to be the slowest op. Its always going to be clumsy. I suggest you design a machine in which there is a lower and upper gun so turning is not needed. I like the angled bed as this uses gravity to set the timber positions on posts. Plus it makes lifting easy. So if you designed a slanted machine with a top and bottom single gun no turning needed. Two stations like the pallet machine and this will produce pallets very fast. Your getting a lot of input here!! What production rate do you need? :) Peter

Hello again. Sorry for the delay, I have had a very difficult week at home.
How much information, thanks!

Peteeng, it is expected to generate around 15000 pallets per month. Working 5 days a week, 8 hours a day. Approximately 100 pallets per hour. Each pallet should take about 40 seconds. You have to take into account the (manual) loading time of nails in nail guns and possible setbacks, you can even add overtime hours daily to adjust to the monthly amount, but I think 40 seconds per pallet would be a more than acceptable value , especially with a model that works in series.

In fact, I would like to automate the loading of the woods onto the mold in some way to further automate production.



Currently the process by hand is done in 2 stations, in this order:

-1: in the 1st station a long wood is taken and 3 cubes are placed, they are nailed and this piece is passed to the next station:

https://i.ibb.co/54wqXSn/Captura-de-...s-15-43-06.png

* (That is why I did not plan to nail from below, I would place these premade pieces)



-2: in the 2nd station 3 pieces of the previously generated are placed parallel to the X axis (I assign an axis so that you can understand the positions). On them, 3 woods parallel to the Y axis, and nailed.

https://i.ibb.co/kG5Dvj3/Captura-de-...s-15-43-14.png



-3: finally, 3 other woods are placed again parallel to the X axis, they are nailed and the pallet is ready to be removed and stored

https://i.ibb.co/0FVYqMb/Captura-de-...s-15-43-24.png




Both stations are widely used wooden tables, not precise at all, and are slightly inclined for comfort. The work is done entirely by hand (with pneumatic nail guns), and the final quality depends on the operators. In fact, the position of the wooden pieces is checked on each pallet by eye.

I want to improve this, and I think there is a lot to work on.

NIC77, I like the idea of ??tilting the machine to ensure the position of the pieces on at least one side.
Later I will think about how to make the pieces fit and stay firm in one position, perhaps with springs or small servos, but it is not a priority now.

I also take the recommendation to use a belt instead of a screw.
Now I am seeing models and brands (it is all new to me).

I like being able to change the speed / torque ratio by changing the diameter, it is much easier than changing a gearbox.


Oh! Another reason why I considered putting 3 guns in place of one on the Z axis is that the nails will last longer. Reloading will pause production and if I can minimize the number of times I will, it will be better.


I apologize again for delaying responding, I am somewhat busy with some personal issues and it is difficult for me to dedicate the time it requires to this project, but I do not want to cancel it either.

I will review your comments again and think how to do magic with my boss's budget.

Hi Gabriel - That's quite a fast cycle time. You will need to get guns with very big nail cartridge's as this will be a set back. How many people to run the cell? I think you will need two lines to get to this takt time. Peter

Quote:

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Originally Posted by Gabrieltaliano

it is expected to generate around 15000 pallets per month. Working 5 days a week, 8 hours a day. Approximately 100 pallets per hour. Each pallet should take about 40 seconds. You have to take into account the (manual) loading time of nails in nail guns and possible setbacks, you can even add overtime hours daily to adjust to the monthly amount, but I think 40 seconds per pallet would be a more than acceptable value , especially with a model that works in series.

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[8 hours x 60 min/hour x 60 sec/min x 5 days x 4 weeks] / 15000 pallets = 38.4 seconds

Do your employees not get two 15 minute breaks during an 8 hour shift? Are you trying to kill the poor operator of this machine? I think Peter was more diplomatic by asking how many employees would be working in the cell.

If I understood correctly, 3 nails in the middle board plus 3 nails on the top board at each joint...

6 nails x 9 joints = 54 nails per piece. If you look at the Stakma Palletmax 6000 video, it takes about 1/2 of a second for a pneumatic actuator to drive in a nail.

With a single air nailer, 54/2 = 27 seconds just to drive in the nails.

Assuming that you can get 3 air nailers all driving in nails in unison, 54/(2x3) = 9 seconds.

To get the cycle times you want, you would need to automate more of the process. For example, your jig holding the boards in the correct position could be automated to let go of the skid when done where it would slide off the table onto a conveyor. Or it drops down somehow, allowing for another skid to be made on top, and eventually you have a stack of skids under the machine.

This kind of automation costs time and lots of $$$. Adding extra features means extra safety features are needed so you don't hurt your poor employee(s).

If you were to buy a Stakma Palletmax 6000 as shown in the video I previously posted, you would still not be able to achieve the cycle times your boss expects. So to think that you can do better on a budget of $4K...it's a ridiculous thing to ask for.

IMO, you should start with a fresh perspective on the whole design process for this, and even the design for your skids, considering every detail including load, unload, and stacking.

This industrial robot can't make your cycle time. I wonder how much one of these costs? Obviously it's alot. It also makes the bottom pieces.

https://www.youtube.com/watch?v=e6kGeKieWeA

This one only moves in one axis (two if you count the air nailers) and then stacks it for you. Really fast nailing too.

https://www.youtube.com/watch?v=sguDGBDGTn4

Hi Gabriel - I used to program IRbs and those in the videos are running slow. But robotics is the go as they can do more stuff in the same place. The cycle times you are talking about require highly automated systems. A full time and motion study needs to be understood to solve your puzzle correctly. Keep at it. Your people equation and safety will be important. The stringer pallet machine is very good (Its Oz, its good). Least motions and less then a minute. Just buy that one...or two you can use your time better then solve puzzles that have already been solved...Peter

Being a clever guy you should also work on getting rid of the pallet. Its a one way, one use device that consumes resources for a very poor reason. Perhaps there's another way for your company to get the product onto a forklift??

about the budget. You need to do a cost analysis of the issue and determine the actual cost per annum of the current system. Picking a random number of $4k for the machine is just a random act. Once the cost is known and the commercial solution costs are known then its easy to say we will make our money back in 6 months a year or 2 years etc. Then you can buy the OZ machine and get on with more important stuff.... as engineers we often get sent down various rabbit holes for businesses and don't solve the issue and we are expected to solve everything even with unrealistic constraints. Impossible is doable but takes a long time. Commercial reality requires commercial solutions...

Quote:

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Originally Posted by peteeng

I used to program IRbs and those in the videos are running slow.

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You're right. I've had some exposure to them at work, integrating machinery next to them.

I have to wonder if it's moving that slowly simply to give the worker on the other side enough time to complete his tasks? If you look in the background, that guy's still loading stuff the entire time.

I just read the video comments on YouTube, and there is an updated version with double the nailguns (4x).

https://www.youtube.com/watch?v=l7zVWqiYNQI

It looks like this one might have two stations on the turntable so you could have two employees loading vs 1 robot. Not sure.

Quote:

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Originally Posted by peteeng

The stringer pallet machine is very good. Least motions and less then a minute. Just buy that one...or two Peter

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I agree. There's no need to over complicate things.

Even the company that makes the robot system says....

"The high flexibility of the robot make small to medium sized orders of pallets optimal. With very low downtime when changing pallet type"

So it's more intended for small to medium sized custom pallet orders and changing pallet types on a regular basis.

Hi - The ekatech robot has a 30sec cycle time. So it hits the business numbers and its not even wound up proper. The Oz machine is probably cheaper then the IRB cell and its cycle time is 50secs. So you buy two Oz pallet makers. If the biz has other duties for a robot then these can be integrated as a backside cell on the pallet cell. Really comes down to the biz and what they are doing and what they need. Gabriel will sort it I'm sure. I think Gabriel said he was in japan. There would be many second hand robots there I'm sure..... An associate of mine has just brought into Oz a second hand 1.2 tonne payload IRB from USA to make into a cnc cell will be exciting!! Its a biggy...Peter