Mars Pro "Set Z Home" seemingly not working

[cliffyk]

I have had a round of email exchanges with "Leon" at Elegoo, a very helpful gentleman. Here is what I found about the z=0 function.

He graciously responded to my initial "What the heck does 'Z=0' do?" query:

The Mars zero reset function is mainly to compensate for the large Z-axis error of the machine during long-term use of the machine, and the size of the Z-axis method of the model is not accurate. Does not have a physical impact on the LCD

https://www.youtube.com/watch?v=cqRBZUAE...rt&index=7

Best regards,

Leon

To which I responded:

Thank you for you swift and informative reply
If I understand correctly it would appear that what I will call the "Z=0" procedure (as shown in the video you provided) is adjunct to the initial alignment provided in the 07/22/2019 User's Manual, in the initial setup process.

in the User Manual procedure:

• the platen locking screws are loosened;
  
• the platen is moved to the Home position with the sheet of paper in place--Z-axis travel is limited by the photo optic sensor;
  
• the platen aligned in the  X-Y axis manually and in the Z-axis by action of the spring internal the the holder;
  
• the locking screws are tightened (front first);
  
• the paper should move freely with just a bit of resistance;
  
• the platen is raised, printing can commence;
  

In the "Z=0" procedure shown in the video:

• the platen is assumed to be in proper X-Y axis alignment (the locking screws are not loosened)
  
• the platen is lowered to the Home position with the paper in place (again I assume with travel limited by the optic sensor?);
  
• the Z-Axis is adjusted logically via the platen positioning controls as needed to allow the paper to move about snugly;
  
• the "Z=0" control is pressed to store the current Z-axis position as a logical end-of-stroke;
  
• the platen is raised, printing can commence; 
  
  

MY further questions are:

From this point (after conducting the Z=0" configuration) is the Z-axis travel limit determined by a parameter saved by the Z=0 function, rather than the optical sensor?

It appears then that the Z=0 exercise is an "in-service" and as "as-required" adjunct procedure to be conducted at times as seen appropriate to validate and "fine tune" the z-axis Home position?

Would/could periodic use of the mechanical alignment procedure from the User's Manual could substitute for, and eliminate the need for the "Z=0" process? Which of course remains a valid quick-check and fine-tuning exercise  

I again apologise for this barrage or questions/concerns, however as a Mechanical Engineer (MSME '1971 MIT, PhD ME 2019 
MIT) with 45+ years experience in data processing it is my nature to know all I can of the machines I use.

Thank you,

-cliff-

Leon replied:

Yes Z=0 is just an additional command program, not related to limit switches，
Prolonged use may result in a 0 point offset, and it is rarely necessary to adjust after completing a 0 point setting.

Best regards,
Leon

So, there it is--the "Z=0" function is an on-the-fly procedure to validate and if necessary tweak the logical "0" position of he platen in-between performing the complete mechanical alignment--I.e. it sets the "0" position to be achieved by issuing the  "G0 Z0" or "G1 Z0" or "G28 Z0" G-Code commands.

The "Home" button will continue to position the platen to the hardware limit switch "0" position.