HOME with absolute encoders

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storen

Storen
I am planning on retrofitting a lathe with DMM servo motors with multi-turn absolute encoders. I consider running it with a MASSO controller.

Is it possible to configure the MASSO G3 to HOME with absolute encoders?

I know LinuxCNC can do that with the HOME_ABSOLUTE_ENCODER configuration setting. I am really trying to avoid using LinuxCNC for this machine and run it with a user-friendly controller such as MASSO.
 
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derekmccoy

derekmccoy
I only know of homing being done with a sensor at the end of the axis. The issue I think is that the position loop is closed between the motor and drive, so while the drive might know its home, Masso doesn't. Maybe there's an output from the DMM drive that can signal it's home or at 0? If so, you could output that to a Masso input and assign it as a homing sensor? Not sure, just an idea. Then again, how does the drive know that the motor wasn't turned more than one turn while it was off?
 
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airnut

Airnut
Storen,

I have been going through a upgrade for a few months now. Perhaps it is the drives that I a using with the Masso, but the information I have in the drive manual says we can not use absolute Encoders. They must be incremental, at least in my case. I really do not know the difference, I do no that compatibility can be a issue.

Regards,

Steve
 
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storen

Storen
Quote from derekmccoy on July 10, 2020, 1:46 am

Maybe there's an output from the DMM drive that can signal it's home or at 0? If so, you could output that to a Masso input and assign it as a homing sensor? Not sure, just an idea.
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Yes, exactly. The DMM Drive has an interface for the encoder information. However, for this to work MASSO has to support this function and be able to read the positional information from the drive.

All major CNC brands use absolute encoders for many years now. DMM made this technology very affordable and accessible to the hobbyist market. The problem is on the controller side. MASSO looks very promising. I am hoping the developers would look into that. Maybe offer it as an upgrade, or by using some third party product?


Quote from derekmccoy on July 10, 2020, 1:46 am

Then again, how does the drive know that the motor wasn't turned more than one turn while it was off?
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It has a rechargeable battery that lasts for years. The encoder will keep counting even if the motor and the drive are off.


Quote from Airnut on July 10, 2020, 1:57 am

They must be incremental, at least in my case. I really do not know the difference, I do no that compatibility can be a issue.
Click to expand...

Incremental encoders are simple counters. They send identical signals. Absolute encoders send unique signals for the different positions of the motor shaft. The signals from multi-turn encoders also contain information for the number of turns. At any moment the machine "knows" the angle of the shaft and the number of turns even when the power is off. With the DMM encoders, the homing would be instant and the accuracy nearly absolute.
 
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derekmccoy

derekmccoy
I meant a pin on the DMM drive that goes high when absolute 0 position has been reached. So Masso would start homing by telling the drive to move the motor towards the home position, the drive moves the motor towards home and the motor encoder starts counting down to 0. The motor reaches 0mm, encoder hits 0, the drive then sends a high signal on a particular pin which is connected to one of Masso's inputs which is defined as the axis homing sensor.
 
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storen

Storen
Quote from derekmccoy on July 10, 2020, 7:00 am

I meant a pin on the DMM drive that goes high when absolute 0 position has been reached. So Masso would start homing by telling the drive to move the motor towards the home position, the drive moves the motor towards home and the motor encoder starts counting down to 0. The motor reaches 0mm, encoder hits 0, the drive then sends a high signal on a particular pin which is connected to one of Masso's inputs which is defined as the axis homing sensor.
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I think I understand what you mean. Basically the home location has to be set in the servo drive instead of the controller and the drive has to have a switching function to trick the controller to think the signal is coming from a limit switch.

I doubt the DMM drives (or any other brand) can do that. This may require a separate piece of electronics specially designed to connect between the drive and the MASSO controller. Probably it would be easier to revise the MASSO software. I mean since LinuxCNC supports absolute encoder homing, it should be possible.

It would be great if someone from the MASSO team joins the conversation and sheds some light.
 
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storen

Storen
Hi Peter. Thank you for joining the conversation.
Quote from MASSO Support on July 10, 2020, 8:09 pm

The encoder is used while threading to track spindle speed and is not used for indexing the lathe spindle.
The Lathe spindle does not home.
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Of course. Homing with absolute encoders is used only for the tool-driving axis and not for the spindle.
Quote from MASSO Support on July 10, 2020, 8:09 pm

The rotary encoder information for the lathe spindle can be found here.
Click to expand...

I am very familiar with this approach. I have the same on one of my machines.
Quote from MASSO Support on July 10, 2020, 8:09 pm

Masso does not support absolute encoders.
Click to expand...

Do you know why your development team decided against adding this function? Is it because it would require too many development resources or the estimated interest in that among the potential users is too low? It is true that very few enthusiasts building CNC machines know about this awesome technology. Until recently the absolute encoders were ridiculously expensive.

I guess the more important question is - are there any plans to add support for absolute encoders in the future? If you have contact with the R&D guys please mention to them there is interest in that.
 
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storen

Storen
OK, after a couple of days researching and talking with the DMM support it turned out it is possible to HOME with absolute encoders using MASSO controller.

The homing location has to be set in the DMM DYN4 drive by using their software and the homing function triggered by sending a simple signal to one of the pins on the drive.

Now I have to figure out how to configure and wire the MASSO controller to send the correct signal. I think it might be best if I start a separate thread for this.
 
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libor

Libor
Can you link the separate thread?

Im interested in this. As well as im interested in using absolute encoder for spindle indexing on milling and possibility of orbital milling. If the controller cant do that i will have to buy something else. And for the technical support... Spindle on all machines now days must be precision indexable when equipped with necessary hardware otherwise the control is garbage. How do you want to do millturn or do any kind of milling on lathe, when u cant index spindle as C axis?

As for the absolute scales, they should be the think commanding positioning, not the encoders on drives. If you have linear scales, u only need servos without encoder as the position is taken from scales directly as well as soft limits should be set in the control system settings and when they are absolute, you should not need to home axis as the machine knows exactly where it is even after power loss. I know how to set those things on Siemens controls, but have no idea how the masso works, therefore trying to find out.
 
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