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### Author Topic: Physical home switches with linear encoders  (Read 569 times)

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#### j2mariashop

• 69
##### Physical home switches with linear encoders
« on: August 14, 2022, 09:30:51 AM »
I have a new Chicago Lathe Bridgemill with linear encoders for absolute positioning of the axes. If the encoder knows its absolute position do I need physical home switches to home the machine? If no, is there a way in Mach4 to set home using these encoders?

#### joeaverage

• 7,570
##### Re: Physical home switches with linear encoders
« Reply #1 on: August 14, 2022, 05:26:15 PM »
Hi,
if using Mach4 then this post belongs on the Mach4 General Discussion Board.....this board is about Mach3. No doubt Tweakie will shift it in due course.

Homing is a realtime procedure that is entirely enacted by the motion controller, not Mach4. When a Home switch activates the machine must respond imediately, or at least
within microseconds. The communication delays from the motion controller board TO Mach4 and then FROM Mach4 back through the motion control buffer would be a delay of
100 milliseconds or more, way, way too slow. Ergo the motion controller must do the job, and is one of the foundational realtime supports that a motion control must offer
to be useful.

Most motion controllers for Mach4, like an Ethernet SmoothStepper can read an encoder, but to my knowledge cannot trigger a Home event based on the output of an encoder.
Remember also that when a machine is Homed or Referenced it is the Machine Coordinates that are zeroed, and you cannot manipulate Machine Coordinates directly, in fact you
can ONLY set them as a Homing or Referencing operation, ie the motion controller alone can set the Machine Coordinates, and the motion controller requires Home switches.

I think Homes switches are in order for a simple and direct solution. I could forsee a couple of methods that might allow the use of linear scales to set Machine Coordinates, but
the complexity counts against them.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'

#### j2mariashop

• 69
##### Re: Physical home switches with linear encoders
« Reply #2 on: August 15, 2022, 10:25:16 AM »
Thanks very much, Craig.

#### KatzYaakov

• 586
##### Re: Physical home switches with linear encoders
« Reply #3 on: August 16, 2022, 01:20:52 AM »
i use absolute encoder with mach 4,its wasnt so easy because you not have simple way to set the current value you read from the encoder
i do all this by external software that read the absolute value from the drivers by Rs485 then update mach registry,then mach take this values and change the homing to " home in position" but put the value as home offset
most work perfect some minor problem
1. for some reason when use home on position cant set motor on reverse
2. for some reason some axes ( the a or b or c ) have some movmevt without any command
this movment are not noise and are not big problem because its not mater of loose position , this small movement are command from mach
so system not loose any position but for example each line you  give G0 x y z ... and a not command but move 0.2mm
and after 100 0r 1000 movement you get software limit for axiss that you not even move it

#### j2mariashop

• 69
##### Re: Physical home switches with linear encoders
« Reply #4 on: August 16, 2022, 10:24:08 AM »
Thank you for the response. Looks like this is a very complex process which ultimately seems to cause more problems than it solves. I'll shelve this in favor of the more practical, and simpler, physical switches. Too bad, it seemed at first an easy thing to do.

#### KatzYaakov

• 586
##### Re: Physical home switches with linear encoders
« Reply #5 on: August 16, 2022, 12:58:05 PM »
It's real powerful ,but sure need alit of practice and tests
Actually who help me alot was steave and wish he will back one day

#### joeaverage

• 7,570
##### Re: Physical home switches with linear encoders
« Reply #6 on: August 16, 2022, 04:32:52 PM »
Hi,

Quote
Thank you for the response. Looks like this is a very complex process which ultimately seems to cause more problems than it solves. I'll shelve this in favor of the more practical, and simpler, physical switches.

Yes, that was my concern that its so complex.

Most motion controllers can read incremental encoders, the familiar A+,A-,B+,B-, but not absolute encoders. The first thing you would have to do is use a microcontroller like an Arduino to read
the encoder. I am assuming the your linear encoders go into some sort of processing/display unit? If they do, it may be that the unit itself processes the absolute encoder inputs and maybe provides
an output on Zero? If that were the case you could use that output to be the equivalent of a home switch, and thereafter you could use standard procedures of Mach/motion controller to
home your machine. It would be an elegant solution, but requires a processing unit to generate a Zero pulse. Does it do so?

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'

#### KatzYaakov

• 586
##### Re: Physical home switches with linear encoders
« Reply #7 on: August 16, 2022, 05:19:40 PM »
I can tell what I do ,I don't know other
I create c# application that conect by rs585 to all devices on chain ( normal 6 servo pack and one inverter,) from servo we read the absolute encoder( it's stored on 7 buffet ,it's took me several howers understand how convert it but now it's work perfect
One big advantage it's that Mach it's not real time system but this absolute give me the options to compare in any time between what Mach think and what is real

#### Cbyrdtopper

• 900
##### Re: Physical home switches with linear encoders
« Reply #8 on: August 17, 2022, 08:53:01 AM »
I was going to suggest something similar to what Craig said, looking at the unit itself.  Some servo units that use absolute encoders have their own homing process that they can do internally, all they need is an input to tell it to start.  If you can do that with the servo drive, you may be able to home the motor with the unit and then have Mach use the home in place feature once you get a complete signal from the servo drive unit.