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MEW Stepper Power Cross Feed stops

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Daggers03/11/2018 16:55:25
14 forum posts

Hi All,

I constructed the stepper motor electronic project as shown in MEW issues 118-119 and redesigned the attachment to fit the Warco type WM14/16 milling machine.

This conversion has work great for the last 5 years, i am at the moment doing a strip down clean,adjust and adding an Ardunio wifi dro upgrade to the mill.

One modification i would like is to incorporate end stop switches. I am not an electronics expert so i am not sure how to achive this, if it is possible.

Is there someone who could advise

Thanks

dcosta03/11/2018 22:02:57
447 forum posts
203 photos

Hello Daggers, good evening.

First of all I must say that I am not an electronics expert.

One possibility is to use a Hall effect sensor (very small) fixed at each end of the course of the cross slide and a very small magnet fixed at each end of one side of the cross slide.
The sensor is very easily understood by the Arduino and the necessary code exists available as an example on the WWW.


I am experimenting with the use of Hall sensors and magnets (4mm diameter and 2mm thickness) to detect and control movement of a disc mounted on the spindle of the lathe and using the information gathered to control the rotation of the lead screw.
The Hall sensor I use has the SS49E reference.


Additionally, I call your attention to a driver that I am also using in this experience that has also proved very easy to use with Arduino. It is currently controlling a stepper motor and the programming was also easy (perhaps because I was professionally a programmer). That driver is referred to as TB6560.

If I can help you please feel free to ask.

Note:
Not being English my mother tong perhaps I wrote some wrongs or was not clear enough. If so I beg you, please, forgive me.


Best Regards
Dias Costa

duncan webster03/11/2018 22:39:25
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2232 forum posts
32 photos

I used microswitches and relay for end of travel and stop switches on my mill table drive. Seemed better to rely on hardware for something that has got to work or it gets expensive. Arduino takes care of speed and ramps. Might not be applicable to your situation but send me a pm if interested

Zan03/11/2018 23:20:16
98 forum posts
2 photos

I would go for microswitches or optical, magnets with all the swarf about would get plastered with tiny bits, not a good idea. On the lathe spindle it’s another matter. Was thinking about something similar myself, but I’m running out of years.....

Joseph Noci 104/11/2018 06:37:13
542 forum posts
832 photos

Hi Daggers,

It is not to complex to add switches to your setup. If you can do some basic software programming, then it can be done quite neatly. If not, you could achieve the same end with some micro switches and what I term a 'bypass'

Fit microswitches at each end, series the normally closed contacts of both , and feed the stepper pulse through these contacts to the stepper driver. When the uswitch is activated, the contact opens and the pulses no longer reach the stepper driver, so the stepper halts. Then you need to fit a momentary ( push-to-make) switch across both microswitch contacts, so that when you press it, it allows the stepper pulses through again, so that you can back the axis off of the activated microswitch. Once the microswitch is no longer activated you release said push-button and carry on with normal operation.

Doing it in the software would alleviate the need for the pushbutton, and you would then just connect the microswitch contacts to a processor input port and when the software sees the contact activate, it stops generating stepper pulses, basically halts the axis 'feed'. Then the software would disallow further auto-feed motion, till the axis is backed of the switch position, and the switch contact becomes inactive again.

If you are not comfortable mucking with the software, the 'manual' switch method is easy to implement; alternatively, I am sure there are other Aurduino aficionado's who may know the MEW project and could assist with some software.

For general interest, these days it is almost not worth mucking about with hall effect sensor and magnets and how to mount the bits, and protect the sensor from swarf, etc - there are many inductive proximity sensors available so inexpensively, all sealed, easy to use, etc - here is an example, and at $3.19, with maybe even free shipping in the UK, it cannot be beat..

**LINK**

Joe

John Haine04/11/2018 07:21:27
2608 forum posts
133 photos

Um , steppers, plus arduino, why mess around with switches or sensors? Just count the pulses.

Joseph Noci 104/11/2018 08:22:02
542 forum posts
832 photos

Without being presumptuous, I took Daggers statement ' I am not an electronics expert so i am not sure how to achieve this, if it is possible.' to mean that possibly he is also not a software fundi...

And anyway, counting the pulses does not work either, as you have no zero reference - the stepper positions in this application are not absolute, so you would first have to move the axis to one end, and set this as a zero reference and count from there, or use an axis centre reference and count plus/minus from there - and you would need a reference switch of sorts to know you are at the reference point.. either way, it is a pain to first reference the table each time you turn on the machine - normal in the CNC world, but not in a manual machine situation.

Joe

John Haine04/11/2018 09:40:00
2608 forum posts
133 photos

Well I noticed that he is "adding an Ardunio wifi dro upgrade" so some interest in DIY computing presumably.

How do you set up mechanical stops? Move the table to say the left extreme of machining, move the stop hard againt the register, clamp. Do the same at the other extreme.

So with processor control: move to say the left to your desired stop position; press a button to zero. Feed to the right by pulsing the stepper; press another button to store the limit. Then the firmware can generate step+direction pulses, incrementing/decrementing a counter only between those limits.

If you just want limit switches at the extreme ends of travel, why bother unless the table will fall off or the screw fall out of the nut? Steppers are tolerant of stalling, though they do make a horrible noise.

Mike Cox's website describes an elegant power feed stop stop system which could be adapted.

Daggers04/11/2018 10:04:10
14 forum posts

Thanks for all the replys,

Can i first say that the Ardunio DRO upgrade is a totally independent DIY upgrade/project and has no association with the power cross feed. I have just stripped the mill to add this DRO so now would be a good time to do any more upgrades.

I would just like to limit add switches at the ends of the travel for safety. I do quite a lot of long passes and get distracted easily.

My problem is where in the MEW circuit can i add the switches without harming the controler etc. Do I just cut power to the controller or is there a better circuit option.

Daggers04/11/2018 10:16:59
14 forum posts

John

I have looked into Mikes stop system and that is just what i would like to add.

And if my power cross feed was an conventional electric motor it would be fairly straight forward.

Having a controller with stepper motor attached I am not competent with electronics to decide the best way to break into the circuit to achieve a safe solution, i.e a gentle circuit stop with damaging any electronics.

Neil Wyatt04/11/2018 10:31:35
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Moderator
16568 forum posts
687 photos
75 articles

I think the simplest solution would be to wire two stop microswitches in series and use them in series across a break in the wire I have indicated in the handset.

mod stepper.jpg

Although this means at least one more wire in the handset cable, this will stop the travel in 'run' mode but allow you to inch the feed (in either direction).

Alternatively just break the pulse wire inside the unit, but then you will need to manually move the feed back from the stops.

A better but more complex solution would interact with the direction switching so you could reverse out. One way would a relay operated by the direction wire to choose between two microswitches so the stop only works in the appropriate direction.

Neil

Daggers04/11/2018 10:44:06
14 forum posts

Neil,

Thats what I’ve lookin for, stopping the travel the change direction on the handset and press inch until switch is overriden.

Although i can build a project i could have looked at that circuit for a year and still not seen the soultion.

The MEW stepper cross feed has worked great over the years but this addition will just give me piece of mind during a long slow cut.

Many Thanks

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