Quick Tip: IF you have Home/Limit Switches, here is an example and description on setting them up

[Dan M]

Just be glad you don't have a CDO problem. It's like OCD, but the letters are in the correct order like they should be.

Haha I like that one Tom!! See you really do learn something new everyday.

[Racedirector]

Quick question on this subject....

I don't have a limit switch on Z yet, I have been just jogging Z to it's highest point and THEN I activate the homing sequence which in LinuxCNC would automatically set Z to Zero (0). Is that the same here for Acorn?

Cheers
Bruce

[Gary Campbell]

Quick question on this subject....

I don't have a limit switch on Z yet, I have been just jogging Z to it's highest point and THEN I activate the homing sequence which in LinuxCNC would automatically set Z to Zero (0). Is that the same here for Acorn?

Cheers
Bruce

Yes it will, but don't underestimate the value of the Z homing/limit switch

[Racedirector]

Thanks Garry

Plans are afoot to get a proxy onto the Z, I need to sort out proper dust collection first and that has to wait until I move into my new house and get my large shed built

Cheers
Bruce

[hardy9000]

Hola tengo este inconveniente a la hora de configurar los swithe the home

[hardy9000]

Buenas alguien me podria facilitar un post procesador para master cam

[richardb15]

I've read this thread and maybe there is some confusion about home/limit, as normally they are two different things at least on the CNC machines I've worked on. I've also got a question on the wiring suggestions in this diagram for Acorn6 and multiple drives:
https://www.centroidcnc.com/dealersuppo ... 147.r2.pdf

Normally I'd expect that each axis would have one home switch, set to go NO perhaps 10mm from one end of the travel for each axis. This gets used by the controller to seek out on startup and set machine zero to a repeatable and known position. Usually it also sets the software travel limits as it gives the controller a known position to work from.

Each axis will then often have either 1 or 2 limit switches on each axis, set to go NO perhaps 1-2mm from hitting the extreme overtravel position for each axis. These are used to disable the drives in the event of software parameter or some other failure that stops a drive runaway from causing the machine to lock up, burn out motors etc. With 2 switches per axis one is at each end, with 1 switch per axis (usually just past the home switch) that end is the hardware disable, and the other end overtravel is set as a machine parameter in the software. Safer and more robust to have 2 physical switches per axis.

In the schematic linked above all the home switches are wired in series into connector H4 IN1, and all the limit switches are wired in series into IN2. All drives are enabled from H14 "all axes enabled" and wired directly to ENA+ all drives in parallel. I don't understand the logic of this, as it relies totally on the Acorn6 to be awake and functioning to enable/disable the drives. I would have expected that each axes overtravel limit switches would have been in the relevant enable line for that axis, so an overtravel breaks that signal and stops the drive regardless of Acorn6 state, but only disables the drive that has gone to its limit. A temp over-ride push button is generally used to energise the disabled axis or axes and allow the user to jog off the switch to restart the operation.

How have others wired limits and separate home switches? I'd be very nervous not having a physical switch to break drive on any axis before it runs off the ends of travel, software is great all the time it works, but that is not guaranteed.

Cheers,
Richard

[centroid467]

They are normally two different things but we've made our systems to be flexible enough to handle most cases. For instance, we typically recommend routers just use one switch per axis set as Home and Limit and then use the software defined limits on the other end. Some of the options make more sense on the Acorn where there are only 8 inputs without an additional expansion board. This schematic is a sample of a working configuration for the hardware shown. There are other ways to wire it, including separate positive and negative limit switches with an additional home switch per axis. You'll notice that there are separate open-collector enable outputs per axis on H1-H4 - there is nothing stopping you from using those instead of the Enable All on H14.

I'm not sure about disabling only one drive - current Centroid systems do prohibit that axis from moving under a programmed move once a limit (switch or software defined) is reached. I think this would be accomplished by halting the position commands while keeping the drives enabled. After the limit is reached, you can move the axis away using incremental or slow continuous jogging moves commanded from the VCP, pendant, jog panel, MPG, or other applicable sources.

Wiring the limit switches in series with the Drive Enable signal sounds like it would be more useful on other controllers. Centroid systems are designed to handle the travel limits as explained in the previous paragraph. The g code parser and plotting functions will let you know if a program will exceed the travel limits.

[ShawnM]

Yes, a home switch and a limit switch are two different things and both serve different purposes.

That said, I'm a router user with two routers, one with Acorn and the latest with AcornSix. Both machines are utilizing the Centroid "soft limits" set up in the wizard and BOTH machines only have a single proximity switch at the "HOME" location for the X, Y and Z axis. There is no need for a 3 axis machine to have more than 3 switches. If it makes you feel warm and fuzzy to have more proximity switches for the travel limits at the far end of the machine you can certainly add these but they take up more inputs. On an Acorn system you only get 8 before you have to spend money to buy more. With AcornSix you get 16 which is plenty for an average router. The only reason to have a second home switch on the Y axis is if you want to use auto squaring.

On my Acorn system with Clearpath servos I have all 3 proximity switches wired in series to a single input (set as the home and limit) and soft limits set for the max travel distance. This has never failed in 6 years. On the latest router with AcornSix and DMM DYN5 servos I have all three proximity switches wired to 3 different inputs (set as the home and limit) and again using soft limits to set the max travel distance. The AcornSix router has a gantry that easily weighs well over 1000 pounds (yes, just the gantry) and it stops every time even traveling at 1350 IPM rapids when moving to the soft limits.

As noted by Centroid467, there are a few different lines of thinking on this and Centroid allows for various options. You can wire it however you want and make it as complicated or as simple as you want. I choose the simple method for my builds.

After you start up the machine and home to the switches the software now knows the physical travel limits or envelope of the machine. Barring you you dont have steppers that miss steps it'll never travel outside these limits or trip a limit switch. When you load your g code the first thing you should do is press F8 and graph that job. The software will either graph it and you are ready to start or it'll tell you if the current file wants to travel outside the machine envelope. If this is the case, then you get an error message telling you which axis is outside the travel limits. You'll get this error BEFORE you even start the job. It doesn't get any simpler than this.

It makes no sense to me to have a limit switch break the enable signal to a drive. Then you'd have to rehome the entire machine and start over. I also have also never used or retrofit a CNC router with a pushbutton override to enable a drive. Mind you, I only retrofit commercial routers not hobby routers.

The Centroid system just works as designed and I try to not reinvent the wheel when it's just not necessary.

[richardb15]

Thanks for the inputs and thoughts. I'm coming into Centroid from old school commercial CNC lathes and mills running Heidenhain, Anilam, Fanuc, EZPath etc and it is almost universal for those industrial machines that separate limit and home switches (usually in the same switch body) are used, I accept the "new" way of doing it may be different, hence asking before doing.

In terms of using a physical switch to disable a drive at extreme limits, yes you'd have to rehome, but that is much less hassle in the event of a screw-up than having ball screws run off or to hard stops. If one is hit, again its common to have a momentary pushbutton to override and allow the user to jog off the extreme limit switch. I guess after 30 years of seeing CNC machines do odd things due to faults I have little confidence in software controlled limits! I've no idea how commercial routers are usually set up, never used one.

All good, thank you!