Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: rabphxaz on November 18, 2008, 07:23:51 PM
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OK, I totally don't understand the soft limit setup. If I define my XY work space as a 22" x 44" area that has limit switches 2" outside of that, and the Y axis has a 7" height with 1" to the limit switches above and below that, and I want to have soft limits 1" outside my XY work area and 1/2" above and below my Y, with a slow down setting of 1/2", shouldn't my Soft Limits settings be:
X Soft Max: 45
X Soft Min: -1
X Slow Zone: .5
Y Soft Max: 23
Y Soft Min: -1
Y Slow Zone: .5
Z Soft Max: -7-1/2
Z Soft Min: +.5
Z Slow Zone: .5
When I do this, I can still jog right past all of the soft limits. And, what is Home Off.? And also the manual says, "the defined limits only apply when switched on using the Soft Limits toggle button -- see Limits and Miscellaneous control family for details." Where the heck is that??? Anybody?
Thanks again, Bob
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So your limits are at 0 and 26 for the Y............ 0 and 48 for the X ? ? ?
Soft limits should be 1 and 23 " 1 and 45 "
This button toggles the soft limits on/off...Green border when ON.
RC
"Home Off" is where you enter the value that you would like for the DRO to display after the homing routine is completed.
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No, what I think I want is that the work space is defined by the X being from 0 to 44, the Y being from 0 to 22, and Z being from 0 at the top and -7 at the bottom. If the soft limits and slow down are going to be outside of that area, then they would be, I think, at the locations I listed. Part of the problem, I just discovered, is that my manual doesn't have the soft limits section that was copied in the other post. I will go play with that, but if you would let me know if the way I'm thinking about it as referenced in the previous sentence, I would appreciate it.
Re: Home Off., in my case, that would be 000, wouldn't it?
Thanks again, Bob
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Sorry, that should read, ...." but if you would let me know if the way I'm thinking about it as referenced in the previous sentence is correct...."
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Limit switches are at 0 in machine coordinates, and can't be at -2. I think the soft limits need to be in machine coordinates as well. Also, your Z min needs to be less than Z max. you have them backwards.
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Bob,
1 axis at a time...X.
Do you have + and - limits and a seperate HOME sw. ? If so, soft limits can be a - and a +.
Or does one of the X limits double as the home ? Then both soft limits are +.
Soft limits are relative to the HOME pos in Mach Coords.
Home the axis, then jog to where you want the soft limits to be in Mach coords, copy the DRO values into the Soft limits table.
RC
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Tell us a bit more about your setup such as limits and home switches like RC has asked, also which position relative to the tool that your home switches are.
I dont really know what RC is meaning but Softlimits should always be Zero for X and Y min and Z Max and the axis travel for X and Y Max and Z min (X and Y being a positive number and Z being a negative number). If your switches are other than at the Machines Zero position (see diag below) then you set a Home Off value to tell Mach that. In the drawing the quill is fully up and that is Z zero, the table is fully right for X zero and fully towards you for Y zero.
If you dont have.zero for the X, Y min and Z max then you will need to disable softlimits each time you home.
Hood
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Hi Hood,
I was referring to the original post. Looked like he wanted the Soft Limit 1" before the switches.
SoftLimits +1 and +45 .... Switches at 0 and +46.
Really need to know how he is configured.
RC
Also, I agree with Hoods procedure. I have this clip saved in my "Pertinent Notes" folder.
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Has ha RC you could have edited my typo for me ;D
In the situation above I would set a Slow zone to be 1 inch and that way the axis would start to slow down 1 inch before the axis extent however its probably not needed to be that large but that will depend on axis Accel/Decel.
Hood
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Okay, I'm back after a computer meltdown. If it isn't one thing it's another....
I have reread all the posts re: this subject several times now, and I still need some clarity. Firstly, unless I have completely misunderstood some of the posts, it seems that there is some disagreement about the Z axis and whether it is standard for the Z zero to be set at the high part of its range, and everything below that (closer to the table) is negative. Others seem to think that Z zero should be set at the work surface, and everything above that should be positive. In the case of the Z zero at the top, a soft limit above the Z zero position would be positive, but it would be negative if it is set below the low position. In the latter case (the Z zero is at the work surface), the soft limit would have to be negative if it is below the work surface. The problem as I see it with the first configuration is that you have to work with negatives, measuring down from your tool bit and then adding another negative number to that to get the cut depth you want. The problem with the second method is that if you want your tool to go home after doing a procedure, or to get ready for another procedure, it would travel at the height of, and/or end up at, the work surface, making it hard to remove the work and possibly damaging the surface of the material.
So, let's solve that first.
As to Hood's question about my machine orientation, the lower left corner of the XY axes is near the operator and on his left. As of yet, there are no limit or home switches -- this is why I want to get this soft limit thing correct.
Is it possible to avoid some of the issues mentioned above by having the soft limits be the home and positions away from home beyond which you don't want to go (that is, what I would consider the usable work surface), and the slow down 1/4 inch, say, before that? The only problem that I can see is that the machine slows down when it is working near the limits...is that a problem?
Thanks again, Bob
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Regarding the Z axis, you are getting confused between machine coords and work offsets. Machine coords has the Z zero as furthest from the table and all movement is negative. However just like for X and Y when you jog down to your work you can set a Work offset zero at the surface and above will be positive and below negative, machine coords will still be all negative though and you can confirm by looking at them.
Your X and Y are correct for home position, well I say correct as in industry it tends to be the opposite for the Y but they use a Home Off value so when they home the machine knows it is + full travel. You could do the same in Mach but if you are happy with your homes that way then you dont need to :)
Hood
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Oh wait a min are you meaning the cutter or the table is nearest you? My pic is actually wrong in a way as the dot is showing the correct position for the X and Y zero but I should have had the table in to the column.
Hood
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Okay, I'm back after a computer meltdown. If it isn't one thing it's another....
I have reread all the posts re: this subject several times now, and I still need some clarity. Firstly, unless I have completely misunderstood some of the posts, it seems that there is some disagreement about the Z axis and whether it is standard for the Z zero to be set at the high part of its range, and everything below that (closer to the table) is negative. Others seem to think that Z zero should be set at the work surface, and everything above that should be positive. In the case of the Z zero at the top, a soft limit above the Z zero position would be positive, but it would be negative if it is set below the low position. In the latter case (the Z zero is at the work surface), the soft limit would have to be negative if it is below the work surface. The problem as I see it with the first configuration is that you have to work with negatives, measuring down from your tool bit and then adding another negative number to that to get the cut depth you want. The problem with the second method is that if you want your tool to go home after doing a procedure, or to get ready for another procedure, it would travel at the height of, and/or end up at, the work surface, making it hard to remove the work and possibly damaging the surface of the material.
So, let's solve that first.
As to Hood's question about my machine orientation, the lower left corner of the XY axes is near the operator and on his left. As of yet, there are no limit or home switches -- this is why I want to get this soft limit thing correct.
Is it possible to avoid some of the issues mentioned above by having the soft limits be the home and positions away from home beyond which you don't want to go (that is, what I would consider the usable work surface), and the slow down 1/4 inch, say, before that? The only problem that I can see is that the machine slows down when it is working near the limits...is that a problem?
Thanks again, Bob
I think your mixing home positions, machine coordinates, and work coordinates all together. The home position can be where you want it to be. It is probably most often set to one corner of the X/Y travel, and, I think, *always* full up on Z. Work coordinates are generally zeroed somewhere else that is on, or at least relative to, the actual workpiece. It is conventional for Z=0 in work coordinates to be the top-most surface of the workpiece. Moving Z in the minus direction always moves the tool downward. If you have no home switches, then machine coordinates have relatively little meaning, and you can define machine zero to be wherever you like on a job-by-job basis, and set work coordinates to be the same.
Regards,
Ray L.
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Well, that helps. If I forget about home positions and work coordinates, and concentrate solely on machine coordinates in order to set my soft limits, then could I dial them in kind of like what I talked about in the previous post, that is, the soft limits and the max and min machine coordinates are the same, with a 1/4 inch slow down in front of them?
Thanks again, Bob
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Bob
If you dont have home switches then you can still use the softlimits but for them to be of any use you will need to simulate a homing operation. What you can do is have marks on each axis at their extremes and move to them by jogging. Once you are there then you can press Ref All button and if you are looking at machine coords you should see all DROs go to zero, that is you now homed. You can now set up softlimits and slow zones as required.
It is important to know where your tool is in relation to your home position as that will determine whether you need to set a Home Off value for any of your axis. If your Axis did not zero in Machine Cords when you pressed the Ref All button then firstly make sure you are indeed looking at the machine coords by checking the machine coords button has been pressed and is active. If that still doesnt show the DROs being zero then go to Config menu then Homing and Limits and check the Auto Zero is chosen for each axis.
Once you are fine with all that then you are all set and you can enable the SoftLimits via the button on the main page in Mach.
Hood
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OK, thanks, I'll work with this and see what happens. Hood, I see that you're from Scotland, you ever read any George MacDonald Fraser, my favorite author?
Bob
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afraid not, cant read ;D
Hood
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Well, if you ever decide to learn, give Fraser a try -- his Flashman series is the funniest stuff I've ever read.
Thanks again, Bob