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WM16 Mill Arduino Power Feed

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Tom Gullan14/03/2018 22:01:54
81 forum posts
25 photos

Hello,

I recently designed a power feed on the X axis of my milling table using a wiper motor and a PWM. Everything works fine, however as yet I have not incorporated some sort of failsafe device like micro switches to stop the motor before the table reaches its maximum travel in either direction.

I am thinking of using an Arduino Uno micro computer along with some sort of sensor setup on the lead screw to count the amount of turns on the screw. I would then be able to write a program to count the turns and stop the wiper motor before the end of the travel.

I would be interested in hearing from anyone who has done this or who has any thoughts on how to do it.

Regards

Tom

John Rudd14/03/2018 22:11:26
1282 forum posts
57 photos

Rather than count the number of turns, just use a switch positioned to detect the end of travel?

The switch could then be placed anywhere along the axis for smaller travel jobs?

Emgee14/03/2018 22:44:36
934 forum posts
187 photos

Hi Tom

As John suggests use a switch or even 2 switches, set to each end of travel required, by using dpco switches or perhaps switched relays you can have auto feed fwd and rev.

Emgee

duncan webster14/03/2018 22:48:52
avatar
1776 forum posts
31 photos

Tom,

I've used an arduino to convert lead screw rotations into distance travelled, it was written up in either ME or MEW, You can find it online at

**LINK**

You'd need to write more code to enable end of travel. However if all you want is to set end of travel, then microswitches are a lot easier, My miling machine table is driven by arduino and stepper motor, but microswitch end of travel as I reckoned it more relaible.

John Haine15/03/2018 07:14:00
2191 forum posts
126 photos

If you really want to use an arduino for this then why not use a stepper motor and driver instead of a wiper motor?

XD 35115/03/2018 08:46:54
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1115 forum posts
59 photos

I would use a 555 timer set up as a one shot with a time base of 1 hour and use centrally located micro switch unit to trip the reset pin of the 555 timer . You can then use adjustable end stops like on a commercially available power feed to stop the table where you want , you may only want a 100mm of travel on some jobs and more on others . The stops also act as end stops for full table travel when set at each end of the table . The 555 simply activates a relay to power up the pwm controller .

I made a power feed controller for the z axis of my mill using a pwm and an arduino nano that reads the pulses froma rotary encoder to work out the feed rate in mm/ min and display it on an lcd screen , it uses a micro switch end stop and an adjustable stop on the quill feed rod so i can set it to stop where i want .

The sketch is just a slightly modidied tacho sketch i found on the internet and changed two lines of code .

Speedy Builder515/03/2018 08:58:31
1595 forum posts
109 photos

If using a micro controller, then the failsafe should be fixed microswitches at each end of the traverse. If you had a blip in the power, all sorts of things could happen. If using a wiper motor, perhaps incorporate a fuse in the circuit to prevent burn out of the motor.
BobH

Brian G15/03/2018 09:02:34
362 forum posts
8 photos

In order for the Arduino to stop the table by counting leadscrew revolutions it would need to know its starting position. This would either require storing the position between runs, manual setting, driving the table up to a sensor in the same way as a 3D printer, or reliably storing the position.

Personally I would be unhappy with storing the position as this could fail in the event of an uncontrolled shutdown, or if the table was moved whilst the Arduino was powered down, whilst manually setting the position each time would be a chore, which could lead to damage if forgotten. That leaves use of a microswitch, optical or magnetic sensor any of which could much more simply send a stop signal directly to the Arduino.

Brian

Martin Kyte15/03/2018 09:19:46
1335 forum posts
9 photos

Why not keep things simple and run the motor power through the limit switch(s). Or if you want to get fancy encorporate an emergency stop relay held on by your limit switches and estop switch wired in series.

It's not normal to have safety systems controlled by electronics, computers or uprocessors. You just keep things as simple as possible with contacts that just knock the power off.

regards Martin

John Haine15/03/2018 10:07:41
2191 forum posts
126 photos

Or see here for a well thought out system of adding stops and adjustable power feed, from Mike Cox.

Phil Grant09/10/2018 19:56:25
21 forum posts

I know this is an oldish thread but I'm researching a similar topic for adding a power feed to my Warco mini lathe.

Having had a lot to do with 3D printers and making my own why not look at a non contact inductive sensor as a limit switch, they are used on industrial machinery all the time and don't wear out or get swarf in them or liquid.

Just a thought.

not done it yet09/10/2018 20:56:24
2379 forum posts
11 photos

Belt and braces, but I would still want a mechanical link to fail if the table managed to reach full travel at one end or the other. Switches are OK for control points, but a shear pin does not need anything other than itself to decouple the dive from the driven. Keep it simple.

Phil Grant09/10/2018 21:08:21
21 forum posts

You'll get no disagreement from me smiley

I already added a mechanical stop to my manual autofeed engagement on my Warco super mini lathe as I didn't want to crash the chuck if I got distracted.

Mike Poole09/10/2018 21:15:32
avatar
1573 forum posts
41 photos
Posted by Martin Kyte on 15/03/2018 09:19:46:

It's not normal to have safety systems controlled by electronics, computers or uprocessors. You just keep things as simple as possible with contacts that just knock the power off.

regards Martin

The motor industry has been using electronic safety devices for at least the last 35 years, safety PLCs and bus systems are now common.

Mike

Tom Gullan10/10/2018 00:27:56
81 forum posts
25 photos
Gentlemen,

 

Thanks for your comments. I actually ended up settling for a window wiper motor and a PWM system. Here’s my attempt:

https://youtu.be/X3IV30oOFpY

 

Regards

Tom

 

Edited By Tom Gullan on 10/10/2018 00:30:39

Edited By Tom Gullan on 10/10/2018 00:31:41

Edited By Tom Gullan on 10/10/2018 00:35:44

Phil Grant10/10/2018 06:35:41
21 forum posts

Looks good and it looks like you used inductive sensor for limit switches?

Edited By Phil Grant on 10/10/2018 06:36:05

Martin Kyte10/10/2018 08:39:08
1335 forum posts
9 photos
Posted by Mike Poole on 09/10/2018 21:15:32:
Posted by Martin Kyte on 15/03/2018 09:19:46:

It's not normal to have safety systems controlled by electronics, computers or uprocessors. You just keep things as simple as possible with contacts that just knock the power off.

regards Martin

The motor industry has been using electronic safety devices for at least the last 35 years, safety PLCs and bus systems are now common.

Mike

Cars don't generally have an emergency stop system or safety interlocks on guards. Machinery and system which are generally electronically controlled will have safety systems built in to that level in the form of watch dog timers, system health monitors etc. However the top level Emergency Stop system is generally made as simple as possible and is best when it overrides the electronics and just kills the power/closes the shutter on the laser/etc.

regards Martin

regards Martin

Phil Grant10/10/2018 12:22:53
21 forum posts

I think we're getting a bit over the top here, don't mix cars safety systems and machine interlocks up with each other, each have different requirements.

Early prototype vehicles do have E stops fitted to them but they will only cut out specific systems ..say fuel pump incase there's a fire or the E-Throttle, production vehicles don't have these because the systems have all met certain requirements.

A modern lathe or mill will already have an emergency cutout switch all I would need is a limit switch feeding into the processor, it could indeed drop the power to the driver module but I would not like to put a switch in series with the 240V motor as a limit switch, this would require having mains voltage wiring around the machine and cause a bigger problem than cutters in chucks.

Martin Kyte10/10/2018 12:43:55
1335 forum posts
9 photos

Thats kind of my point Phil I was really only talking about machine tool systems and the like.

There are two levels of control. Normal operation where all is working as it should which may include all manner of limit switches, home sensors etc all of which can happily be controlled by the process control element.
Emergency stops are there as a catch all and should not normally be triggered at all except in an emergency or when the process system has failed. They therefor need to be separate from the processor and act at the top level to cut the power, close the shutters drop the control rods or whatever is appropriate to the system.

regards Martin

Clive Foster10/10/2018 14:06:10
1507 forum posts
34 photos
Posted by Martin Kyte on 10/10/2018 12:43:55:

Emergency stops are there as a catch all and should not normally be triggered at all except in an emergency or when the process system has failed. They therefor need to be separate from the processor and act at the top level to cut the power, close the shutters drop the control rods or whatever is appropriate to the system.

regards Martin

No argument about the need for separate, ideally brute simple, emergency stop systems. But not so sure about "not normally triggered at all except in an emergency". You really need some form of test procedure to verify that the emergency system is working on a regular basis.

I have personal experience of an emergency system not only not being in working order but also rendered incapable of working by ill thought out modifications. Horrifying thing is that I only checked everything because I didn't trust the folk who'd modified the system. Mostly thinking or reliability as, in my view, a rock solid system had been converted into a flaky prima donna. Good job I did look as the thing failed hard sometime later and needed its emergency stop. Worst thing was that clever clogs engineers had included an emergency system verification routine in the controller which returned a permanent OK status. Ooops!

An excellent lesson in the dangers of reworking a fairly complex, imperfectly documented and not completely understood system.

Switches are good being simple and pretty much foolproof in break on failure mode but do make sure there is enough over travel to accommodate slow down and stop. Screw drive should be OK but I have seen micro-switches knocked off on less positively braked systems in high speed tests. Sprung roller actuators are provided for a reason. Ramming straight up to the button may be OK in theory but margin of error is small. The major weakness of a break to actuate microswitch based system is that if the switch is knocked off odds are it will promptly make contact again and drive will resume. Embarrassing.

Clive.

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