Z-axis homing - Y-axis tuning - ClearPath servo firmware updates

If it's working you are probably fine. Those sensors have resistors to limit current. Mesa is well designed so it should protect itself.


While a brake would work, might want to try a spring or counter balance first as those are easier/cheaper unless their is a drop in servo with brake.

Another option would be have your controls and pc on a UPS and to have the machine job to a "park" location where it lowers z before turning off.

Oh, no worries. Thank you for the reply!

Hmm, so the thing I'm using shouldn't actually work or is it just going to be damaging in some way if I run it like that or cause other issues then? It does seem to be working the way I hooked it up but if it's going to wreck something maybe it's not good to run it like that.

Also, where should I place the resistor? I'll see if I can figure out how to go about doing that if it's something I should be doing to prevent damage somehow.

PNP sensors are suggested for 7I76E inputs as the inputs work by sensing a positive
input voltage. PNP sensors supply a positive voltage when the output is active.
NPN sensors connect their output pin to common/ground when activated.

Some NPN sensors will work with the 7I76E because they have built in pullup resistors,
but for reliable operation it best to add an external 2.2K 1/2W pullup resistor on each
NPN output to guarantee a valid high state. The pullup resistor goes from +24V to the NPN
sensor output.

You can check switch operation by measuring the voltage in both on and off
states at the 7I76E input. With a 24V supply I would make sure its >20V
when high and < 4V when low.

There is not any real possibility of damaging the 7I76E inputs unless
you continuously apply voltages > 48V to the inputs.

 

Regarding the brake...

You can buy add-on brakes that work the the Clearpath from Automation 4 Less.  They are specifically designed for Nema23 and Nema34 stepper/servo frame sizes with 3/8" and 1/2" motor shaft sizes.

They essentially go between the servo and the existing mount, and are powered with 24vdc.  When the power is off, a heavy spring engages the brake.  When powered on, an electromagnet releases the brake.

They are not cheap, but neither are they extremely expensive.  Very easy to install, but will require another cable (two wires) to be run through the gantry to the brake, as well as a 24vdc power source and a relay to control the brake on/off. One of the Mesa outputs can be used to trigger the relay with LinuxCNC's "Machine-On" output signal.

www.automation4less.com/product/category...systems/servo-brakes

As was mentioned earlier, a gas spring (or two) would be significantly cheaper, but will require some fiddling and thought to install.  They can get a little awkward to mount as they need twice the Z- stroke length unless you mount them at an angle.

An internet image search for "z-axis counterbalance" should get you some ideas on springs, gas springs, and counterweights.

This gives me some things to think about for awhile. I'm very grateful for everyone's comments and suggestions and the time they took to post here for me. It's very kind.

I'll have to see about getting the proper PNP switch or the proper resistor somewhere. If those switches have a resistor and they work then maybe having two might not be a good idea? I'm not sure, but that's what my dad thought. I do think doing it right would be ideal though. So thank you to everyone for providing all of the information about them. It's super helpful.

The cost isn't really an issue, their price is fairly reasonable if they last, but unfortunately it seems I can't get those breaks delivered to Canada so maybe I can find them somewhere that will deliver to me or at least something like them, now that I know exactly what I'm looking for. In fact, I did a search and noticed there are actually similar ones on the Teknic website here:

teknic.com/products/spring-applied-power...rakes/NEMA-23-brake/

There are a couple things that concern me though which might help me choose between these types of breaks or the counterweight or gas spring breaks. I don't know if those Teknic breaks are as powerful as the other ones and maybe it doesn't matter, maybe they would be fine. I don't know how much force they have to hold so I suppose the first order of business is figuring out how to measure how much force it has to hold to know which break to get. I'm sure there are calculations and math and whatnot involved which I'm no good at so I'll try to do some research and see if it works out.

Another thing I'm curious about is when doing an e-stop if it uses the break and if there is a way to disable that or maybe that's something I would actually have to enable in the first place and it's disabled by default because I have to connect pins in hal. I only want to apply the break when the machine loses all power and not on an e-stop so that it doesn't wear out the break which I'm guessing is a thing. So I'm wondering if maybe there is some way to set it so that it doesn't use the break in an e-stop and only when the machine loses power or if it's just going to be like that by default.

Thank you everyone! This is very valuable information and I really appreciate everyone's time. This is really great. What a nice community. It's all starting to make more sense now with everyone's great knowledge being imparted onto me. Thank you!

swift.gate0199 wrote:

There are a couple things that concern me though which might help me choose between these types of breaks or the counterweight or gas spring breaks. I don't know if those Teknic breaks are as powerful as the other ones and maybe it doesn't matter, maybe they would be fine. 

They'll be fine.  You just pick the one that matches your frame and shaft sizes.

If you want to measure the z-weight, just put a kitchen scale on the router bed.  Let the Z-axis sit on the scale - maybe with a block between the spindle and scale - and that'll get you close enough if you go the counterwight/spring method.

The weight on the scale is not the force the brake has to hold; the brake just has to keep the screw from rotating - which is much less than the actual weight of the axis.  I bet you can hold it up with two fingers.

As Tommy indicated, all methods are some compromise.  Brakes add inertia to the rotating components and length to the servo assembly, counterweights add inertia to the whole moving mass, and gas springs - even constant-force types - can be fiddly to get the value and geometry right.

It all depends on what you feel more comfortable doing.

Hi swift.gate0199,

I am an Application Engineer with Teknic. I ran across your post and wanted to encourage you to contact Teknic’s engineering team. We should be able to provide recommendations regarding several of the issues you described.

You can contact Teknic’s support via our website (teknic.com/contact/) or by giving us a call at 585-784-7454.

Best,
Bradley N. – Teknic OEM Application Engineer

Thank you for the all the help and the info everyone! This is awesome. I really appreciate it.