Start, Stop, Jog !

[apprentice87]

Hi All,

Some time ago i decided to replace the single phase motor on my shaper with a three phase one like it originally had. Soft me threw away the original control gear years ago..

Now, I would like to wire it up with stop, start, and provision for "jogging" too. Now, i know that this is not as simple as it sounds....

First off; If you do it the "simple" way with a NO/NC switch to do the jogging, you can in theory, and i have ACTUALLY SEEN THIS IN PRACTICE, a situation where if you give a quick "stab" to the jog button, there is a "race" between the switch and the contactor, as to which opens first. If the switch wins, the machine will keep running....

Now, I COULD use a selector switch to select "jog" mode, but i know that i would forget to operate it at some stage.

The "proper" way to do it, would be a contactor control relay to work the jog function, to "separate" completely the "run" and "jog" modes. However, this makes things a lot more complicated. I had an idea!!!! [Oh no! you all say!] What would happen if i used TWO contactors in parallel?? One for the running, and the other for the jogging???

Anyone see any snags...

john...

 

[OnOff]

Sounds like a plan there John. So, Long run button - have the hold on circuit on that contactor only via it's NO aux. contacts I assume? And the jog button just to power the coil on the second contactor (with no hold) Ideally I guess have mechanically interlocked contactors or failing that just put an NO and NC block on the back of the Long and Jog buttons? 

 

[Andy™]

the old AM2 circuit used to have a jog function using only 1 contactor

 

[Nicky Tesla]

jog button?   i have no idea what you lot are on about

 

[m4tty]

jog button?   i have no idea what you lot are on about

Me neither .... Jog on lol

 

[apprentice87]

Hi All,

On machine tools, apart from stop and go controls, you will usually have a jog button. If you press this, the motor will run, but only for as long as you keep your finger on it. Idea is to make it easy to change gears without having to try to turn the machine spindle by hand. If the gears are not lined up as it were, a fraction of a second on the jog button, just to move them all a bit, will help a lot!!

john.

 

[Evans Electric]

Its called an "Inch" button around here !  Its for "inching" or "jogging"  a machine perhaps to line up a cutting tool for instance .

If you look at Andy's diagram you'll see that the "Inch" button is  combined Normally open and normally closed , the "Hold on" part of the circuit is disabled by the N/C bit opening .

Here endeth the lesson for today.

 

[SLIPSHOD & SLAPDASH]

European directive 349 vii, Section 22b part77 2009 states this device now has to be referred as a 25 mm button

 

[kerching]

European directive 349 vii, Section 22b part77 2009 states this device now has to be referred as a 25 mm button

correction................................25.4mm button

 

[apprentice87]

Hi All,

Hmm, Yes, but the problem with the circuit shown is this;

When you press the "inch button" in the centre of the diagram, you make the contacts 3 and 4, powers up the contactor coil and break the contacts 1 and 2 which stops the thing "latching" When you release the "inch" switch though, if the contacts 1 and 2 are "re-made" quicker than the contactor "resets" for want of a better term, the thing will run continuously.... Not very safe way of doing things.. I have myself seen a machine do this..

Here is a link to a bit of a case study that all will find interesting...

http://ecmweb.com/content/case-machine-malfunctioned

john...

 

[steptoe]

then the button is not fit for purpose

Hi All, Hmm, Yes, but the problem with the circuit shown is this; When you press the "inch button" in the centre of the diagram, you make the contacts 3 and 4, powers up the contactor coil and break the contacts 1 and 2 which stops the thing "latching" When you release the "inch" switch though, if the contacts 1 and 2 are "re-made" quicker than the contactor "resets" for want of a better term, the thing will run continuously.... Not very safe way of doing things.. I have myself seen a machine do this.. Here is a link to a bit of a case study that all will find interesting... http://ecmweb.com/content/case-machine-malfunctioned john...

 

[apprentice87]

Hi Steps,

Yep, that is what i think, the "standard" simple way of doing it is dangerous.. That is why i think i will use a second contactor for the jog function..

I saw it happen on a milling machine i own. I was messing about with it one day, and i gave what i presumed was the jog/inch button a stab and the machine carried on running... I started and stopped it a few times, and yep, it was definitely the jog button i pressed, cos i got it to do it a second time....

john...

 

[Andy™]

not sure if such a switch exists, but if you had one with 3 positions, with one being momentary, you could wire it as 'normal' (when it makes the stop circuit), 'off' (breaks stop circuit) and momentary 'on' (where it makes only run'. that way, switch to normal, then existing on/off works, switch to off and nothing will happen, switch to 'inch' and inch will work, but more importantly, the stop is still broken when you release it

 

[steptoe]

way I see it, when you stop it should release the run contacts, then JOG should only energise the JOG part of Andy's pic, Im failing to see how this is hard to wire,

maybe its just my mind, but this seems very easy and basic  to me in comparison to most of the machine stuff you guys post up,

 

[Evans Electric]

Never known a problem with the circuit Andy has shown .  Thats the  standard  as far I know , never known it to start and run from the inch button.   

 

[apprentice87]

Hi There,

Granted, it SHOULD not latch and run, but i have seen it in practice and so did the poor sod in the link i gave above; This one; http://ecmweb.com/content/case-machine-malfunctioned

Given that if it DID latch it could cause serious damage to my machine, i would not be a happy bunny.

To tell the truth, i have taken the belt guards off, and when i am setting the machine, i ALWAYS pull it round by hand first. I know the HSE know it alls would have a fit, but so far as i am concerned, if you are daft enough to walk around the back of a machine tool and stick your hands in a moving belt drive, then if you were to actually try to use the machine, you would be dead in a few hours anyway....

john

 

[steptoe]

John, if it doesnt work as per Andy's link then the switch you have is the WRONG switch,

 

[Andy™]

John, if it doesnt work as per Andy's link then the switch you have is the WRONG switch,

it could happen Steps if the contactor doesnt let go fast enough. or the stop makes before the run breaks

 

[apprentice87]

Hi Steps,

Yes, it is right like Andy says... I had it on one of my own machines, ok, granted it had been stood for years and the contactor might have been all gummed up or something, and it certainly happened to the poor chap in the link i gave..

Andy summed it up much better then i could with "if the contactor doesnt let go fast enough. or the stop makes before the run breaks"

I think what you are SUPPOSED to do, is to separate the two functions by modifying the circuitry with a relay to control the inch or jog function. I think i will just fit two contactors in parallel especially as i think it will be simpler and cheaper!!

john

 

[sellers]

Never heard of jogging myself.  Always knew it as inch.