Locking the movement on an electrical motor 3

[Gustavo Silvano]

Hello there!

I'm an electrical engineer and I just mounted a new machine on my industrie. It's composed of a motor turning a shaft. This turn is made when the operator press a button. But due to the inertia of the shaft, when the motor stop spinning, the shaft make a half of a turn. And this is caused by the fact that the motor does not have a break.
This inertia was not taked into account when I was making the project for this improvement, but I want to fix it without changing the motor. Is there a way to do this? An electrical or mechanical one?
I don't know if it's necessary, but here's the project that was implemented.

Best regards.

Gustavo

 

[waross]

Buy a "C" face brake. Remove the motor from the reduction gear. Bolt the brake to the reduction gear. Bolt the motor to the brake. Follow the wiring diagram. This should solve 98% of the issues.
You may chose to install a brake on the final hoisting shaft. A brake on the final shaft will have to handle much more torque and will be much larger and more expensive.
If you build another similar system, consider using a final reduction gear that has a hole in the final gear so that it may be mounted directly onto the final hoisting shaft.
This avoids the cost of chain and sprockets and, more importantly, avoids the possibility of a broken chain dropping the load.

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

 

[3DDave]

A gear motor can have any kind of gear in it. Is there a reduction gear, 1:1, a bevel gear, a hypoid gear, any other type where the RPM of the motor is different than the output of the gear box?

 

[djs]

It is interesting to note back in the day when servo systems were very expensive, we used a VFD and two position switches to perform indexing operation on case packers. When the index operation started, the motor ran at full speed. As soon as the first position switch was made, the VFD shifted to a slow speed, usually around 25% until the second switch was made. The VFD was then commanded to stop. No brake on the motor. Using this system we were able to perform an index of 30 inches in less than 3 seconds with repeatability of 1/16". Perhaps something similar could be used here?

 

[jraef]

You mention it runs on "contrary", which I take to mean it reverses when stopped. That's called "backlash" and is likely the result of poor selection of your gearbox. If the idea of a mechanical brake bothers you, then another solution would be to change your gear box to a zero backlash version, something like the worm drive mentioned earlier.


" We are all here on earth to help others; what on earth the others are here for I don't know.
" -- W. H. Auden

 

[BrianE22]

Maybe I missed this, but does the brake have to hold a load?

 

[waross]

Or you could borrow a couple of truck batteries and a contactor and try Gunnar's suggestion of DC injection.
You can try 12 Volts and then 24 Volts. If you get decent results and determine the best voltage to use you can then spend the money on a suitable DC supply.
Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Gustavo Silvano]

BrianE22, no. The load is not lifted, it's dragged. The wire rope that drags the load gets stretched out and when the operator stop to press the button, the wire rope pulls the shaft where the gearbox is connected.
jraef, the spin that the gearbox do is kind of a lot. Don't know if a backlash can be responsible for all that.
I think that an electromagnetic brake will be the solution.

 

[waross]

Now I like Gunnar's DC injection suggestion even more.
With DC injection you may use a higher current DC to provide a rapid stop and then drop to a lower level DC current to let the backlash unwind slowly. A timer should be adequate. X seconds at higher current and then Y seconds at lower current.

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

 

[jraef]

You don't by chance have a VFD on this motor do you? If so, you likely have DC Injection Braking available already, it's a feature of almost every VFD out there. If not, then there are lots of stand-alone DC injection braking units available on the market. two features that you will want to look for:
1) Automatic detection of the motor emf being zero before applying DC. This is missing on cheap units and leads to failure of the DCIB.
2) Automatic shut off when the motor has stopped. Cheap ones don't have that or just use a timer and that can cause unnecessary added thermal stress to the motor.


" We are all here on earth to help others; what on earth the others are here for I don't know.
" -- W. H. Auden

 

[djs]

The wire rope that drags the load gets stretched out and when the operator stop to press the button, the wire rope pulls the shaft where the gearbox is connected.
jraef, the spin that the gearbox do is kind of a lot. Don't know if a backlash can be responsible for all that.

If that is the case an electric bake or switching to a worm gear drive gearbox is the only solution.

 

[VEBill]

Some of the Rotary Friction Welding machines shown on the 'net have fairly impressive 'sudden stop' capabilities. Hundreds of kg of rotating mass, reportedly 600 rpm. Once the joint reaches the desired conditions: bang. Seemingly a nearly-instantaneous (I know, not really) dead stop. Certainly impressive enough that the videos are all over YouTube.

Not likely applicable in this case. Presented just in case it provides inspiration.

[EDIT] Here's an example (cued-up at 12s in):

https://www.youtube.com/watch?v=MIYJnd2X9eU&t=12s

 

[drawoh]

VE1BLL,

There are table saws that stop when you stick your finger in the blade. I am not sure this is good for the table saw. I am not willing to test one.

--
JHG

 

[analogkid2digitalman]

SawStop is pretty impressive, blade will be damaged:

https://en.wikipedia.org/wiki/SawStop

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

[jraef]

I'm not sure the blade is damaged. The blade stops by jamming a soft aluminum wedge into it. I use table saws to cut aluminum all the time, it's not a problem for the blade. The Saw Stop unit is a one-and-done device however.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[MacGyverS2000]

j, the blade is usually damaged in the process. Broken teeth and the like... teeth can be brazed back on, but the integrity of the main disk is then in question after such a shock.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[waross]

I posted this back on 13 Sept. At the 50 second mark you can see the action and the deformation of the stopping device.
[URL unfurl="true"]https://www.youtube.com/watch?v=E3mzhvMgrLE[/url]

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

 

[jraef]

The real question is however, why is this guy always trying to cut his hotdogs with a table saw when a knife works better?

And hey, nice camera work!

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[itsmoked]

I don't understand why the blade drops from that movie. The movie doesn't show it dropping only the soft-stopper being launched into it and its rotation being arrested.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[3DDave]

Conservation of angular momentum and a compliant mount that releases the locking support that locates the exposed blade.

Now I'm been down the Sawstop rabbit hole. Lots of anger and dismay about that company for their legal dealings.

 

[MacGyverS2000]

Keith,

Activation of the capture mechanism releases the axle, allowing the blade (and mechanism) to drop from the table. I cannot recall if there is a spring, as well, but the blade drops quickly, so I imagine there is.

Dan - Owner

http://www.Hi-TecDesigns.com