What is jogging function of the inverter ? 4

[terwelu]

Hi guys,

I saw many inverter products today equipped with Jogging function. As far as I know, it's the function that can let the operator to do manual operation with the motor. But what is really the purpose of that in real application ? I mean, if the motor can be rotated automatically, why the inverter still provide the manual operation (jogging) ?

Thanks.

terwelu

 

[waross]

Jogging is moving the motor in small increments. It is mostly used to align or position drive elements for connection or maintenance. If a machine that requires motor jogging for some reason is fitted with a VFD, the VFD may facilitate the jogging but it will still be needed.
There is another operating mode called inching. For very large machines that did not lend themselves to jogging, inching was sometimes used. This was the great grand father of invertors. A DC source would be applied to the motor windings in turn be a series of contactors. The contactors may be controlled by a sequencer or manually by a wheel or crank that operated limit switches that controlled the DC contactors.
Consider a large ball mill (possibly over 20 feet in diameter) that must have an access hatch aligned properly when it is to be removed for internal service of the mill as one possible example.
This system could provide a crude stepped square wave that would cause the motor to rotate slowly and under control.
Although jogging with a VFD may be more analogous to inching than to jogging, inching systems were quite rare and the term jogging is more readily recognized.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Thanks Bill!
I heard about that set of contactors being controlled by a cam plus limit switches. Thought it was a funny story. But, you say it did exist IRL?! Do you have any links to such a beast. Would be very interesting to see one.


Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[controlsdude]

Jog
check for correct rotation at startup

some machines require jog movement to check components at certain spots, by slowly jogging to that spot.

Rotate the motor to bring the machine to a certain position

 

[itsmoked]

terwelu; With a VFD you usually set up a jogging speed. Then when you want/need to Jog you press Jog. The VFD goes into Jog Mode, often an idiot light shows this mode. Now when you press Forward or Back the VFD will ramp up to the Jog speed you put in at setup and stay at that speed until you release the Direction button.

As waross mentioned a common reason is to get hatches or doors into position.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

All it really means is a manual over ride of speed control that may be coming from another command source. So when a technician needs to have the motor rotate, he doesn't have to reconfigure the automatic system. Applications would be rotation checking and access hatches or door positioning as mentioned above, but also a myriad of other uses such as belt tracking, web pre-tension adjustment, chain or brive belt slack measurement, pump priming, visual inspection of gear teeth, anything that requires an operation that is NOT in automatic control.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[terwelu]

Hi all,

Thank you all for your information. Very appreciate it !

So in principle, please correct me if I'm wrong, jog function will be (mainly) used for maintenance activities and non-automatic process. I guess it won't be any special purposes to use this function for main activities of the system itself.

Can I take those statements as "rough" conclusion for jogging function ?

terwelu

 

[jraef]

I would.

 

[waross]

Hi Gunnar.
When you and I were young, I had some old textbooks. One scheme rotated the motor in step with the control wheel. I think that if the operator overshot, he could turn the wheel backwards and run the motor backwards, but I can't say for sure about that function.
My library is spread from my place in Honduras across my cabin and my mother's place in British Columbia to our new place 1600 kilometers east in Alberta, and I am in a construction camp 700 kilometers north of the Alberta place. I'll probably be doing the loop in the next couple of months. If I come across the reference I'll try to get it to you.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ozmosis]

Jogging in a VFD is also a term or function that is describing a command that combines a RUN and Frequency in one action.
Most VFD's will require different commands to activate a RUN and speed/frequency setpoint (not always) but a JOG is the combination of the two. More often than not it is a low speed/frequency (about 5Hz) at default and can be programmed to go FWD or REV.

 

[LionelHutz]

VFD jogging is just a frequency setting and is typically controlled by a digital input seperate from the start/stop. It's really just selecting a frequency and starting the VFD. Sometimes, jogging is just used on an application that needs 2 speeds. Other times, it is used to slowly rotate the motor for service/inspection. Two applications I can think of are bucket elevator inspection and conveyer belt inspection. For both, they need to be run slowly while someone inspects for damage.

Gunnar;

They're not a myth. The scheme works very well for positioning a ball mill powered by a brush type sychronous motor. The contactors make a pretty light show. Attached is a short cut from the video. I'd have psoted a longer better quality clip on a sharing site but we're not allowed to access those sites here... so I spent well over half the morning cutting the video until it would upload directly instead.

 

[itsmoked]

Awesome!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Great video. When I worked for Motortronics we did a number of inching systems for synchronous ball mills like that. I have a video on a disk somewhere as well, one of which was a "before" shot where they used contactors like this. If I can find it, I'll show it.

Gunnar,
Think of it as a very crude form of electro-mechanical cycloconverter.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[edison123]

lionel

Can't see the vid in windows media or apple player. Is there another software for that video ?

 

[jraef]

I had to save it and launch it from the video player itself, it wouldn't play in the browser. Happens sometimes with avi files.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[itsmoked]

I couldn't get it to run in WMPlayer and in AVI only the first second had sound. So I ran it in RealPlayer. Worked fine.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Nice link, Lionel. Thank you for posting it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DaveAlford]

With most VFD's I've used,( even basic ones) you can accomplish the same function without having a "Jog Feature". As long as there are a couple of digital inputs, and the ability to change the speed reference parameter based on the state of those inputs.

 

[macmet]

I got that video to work in Winamp.