DC-1 Limit Switch Issue

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polaraligned
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DC-1 Limit Switch Issue

Post by polaraligned »

I have been using a DC-1 to drive my W axis (knee) for a number of years. It works fine. I decided to add a limit switch as it gets jammed if you move a little too far on it's travel, and I might want to be able to wire it into the PLC in the future to be able to home the knee and possibly use it for tool length offsets.

I wired the limit switch to the + limit input and put the switch at the top of the column to set the + travel limit. Issue here is that the switch does nothing when the knee is traveling in the + direction and it trips with an error "W axis position error" followed by a "327 Fault: job canceled" error when the knee is going in the - direction and I press the switch. I think the error is probably because the drive is not expecting the the + switch to ever be tripped when it is traveling in the - direction. If that is the case, the problem becomes why doesn't the drive stop when I trip the switch during + travel?

I swapped the switch to the - limit input on the DC-1 and the behavior was as described above, but in reverse.

Because these DC-1 drives don't interface with the PLC, there is no input to set and the behavior I would expect would be that they just stop motion and allow you to back off a limit. Is this a correct assumption?
polaraligned
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Re: DC-1 Limit Switch Issue

Post by polaraligned »

So today I added temporary limit switches to my DC-1 running my A axis. The behavior was the same as for the DC-1 driving the W axis. The switch, in the opposite direction of travel, triggered a fault with "job canceled" and the switch in the direction of travel did nothing. I did this for both directions of travel and the result was the same but the opposite switch triggered the fault.

One thing I did notice is that when you trip the limit switch that the drive expects to see for that travel direction, the sound of the motor changed slightly, but kept on moving. So the drive is seeing the switch and doing something, just not stopping the motor...

I am stumped. There is no setting I can find and it is my understanding that the DC-1 drives handle the limit internally and the PLC is not involved.

The limit switch inputs just don't stop the drive motion.
cncsnw
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Re: DC-1 Limit Switch Issue

Post by cncsnw »

The DC1 switch inputs are working correctly. At the DC1 hardware, "plus" and "minus" are the hardware direction, not the logical software axis direction.

Your report shows that you needed to set Direction Reversal = Yes for your fourth and fifth axes. That means on those axes, the software axis direction is opposite the internal hardware direction. Therefore you need to wire the switch at the "plus" end of the axis to the drives "minus" limit input, and vice versa.
polaraligned
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Re: DC-1 Limit Switch Issue

Post by polaraligned »

cncsnw, I greatly appreciate your response and it makes sense. I did try reversing direction yesterday to no avail. I tried again just now.

I installed another limit switch on the DC-1 so I have 2 switches (+ and -) right in front of me to do testing.

The W axis:

With direction reverse set to N, the knee travels up on negative moves.

When I command a negative move:
- Positive switch does nothing
- Negative switch causes a 410 positioning error

When I command a positive move:
- Positive switch causes a 410 positioning error
- Negative switch does nothing

With the direction reverse set to Y, the knee travels up on positive moves.

When I command a negative move
- Positive switch causes a positioning error
- Negative switch does nothing

When I command a positive move
- Positive switch does nothing
- Negative switch causes positioning error

I am ready to jump....this was the first in a bunch of upgrades I have planned for this mill.


Thank you.
Scott
cncsnw
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Re: DC-1 Limit Switch Issue

Post by cncsnw »

That all looks exactly as it should be.

There is not going to be a "407 W ... limit tripped" message, because the DC1 limit inputs are not PLC inputs. They are only hardware inhibits that will prevent the drive from applying current in that direction.

If you need the limit switches to appear as PLC inputs, then you will need to wire them to PLC inputs instead.

It is probably possible to wire them to the DC1 drive inhibits, and also to Allin1DC or PLCADD1616 PLC inputs, in parallel; but you would have to find out what the DC1's pull-up voltage is (probably 5VDC) and configure at least one bank of PLC inputs to match.
polaraligned
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Re: DC-1 Limit Switch Issue

Post by polaraligned »

Thank you cncsnw.

I guess what threw me is the fact that the E-stop contactor trips when the limit switch is hit. Of course it would be nicer if the machine just stopped motion without a contactor trip and the resulting reset that needs to be performed.

What appears to be happening is when the switch is tripped, the drive stops, the MPU encoder inputs are looking for motion and getting none, so the system faults and the E-stop is tripped. Crazy setup.

If the input is paralleled back to the PLC per the manual, the contactor tripping can be overcome with some PLC programming?
xr4x4ti
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Re: DC-1 Limit Switch Issue

Post by xr4x4ti »

You didn't ask for my input, but I am going to give you an opinion.

If your knee is powered, I would think you would want it to home in the - direction, as far away from the spindle as possible. That way when the machine homes, it is moving away from the spindle and less likely to crash.

I have a bed mill, where the table is fixed and the head moves up and down. The head goes up "+" to the extreme of travel to home for the same reason.

Just a thought,
Tim
polaraligned
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Re: DC-1 Limit Switch Issue

Post by polaraligned »

xr4x4ti wrote: Wed Mar 17, 2021 9:40 am You didn't ask for my input, but I am going to give you an opinion.

If your knee is powered, I would think you would want it to home in the - direction, as far away from the spindle as possible. That way when the machine homes, it is moving away from the spindle and less likely to crash.

I have a bed mill, where the table is fixed and the head moves up and down. The head goes up "+" to the extreme of travel to home for the same reason.

Just a thought,
Tim
Tim,
I respect and appreciate everyone's opinion and thoughts.

I did carefully consider homing to top vs bottom. I was going to install limit switches on both top and bottom, but now I will just leave the top (+ direction) in place and use soft limits for the negative travel. Crashes were a careful consideration, but with no tool the knee will home with 7.5" between the table and the spindle, enough to clear a Kurt 6" vice easily. The quill has 5 inches of negative travel. What I will do is put a message in the .hom file that will tell user (me) to make sure there is clearance and will require a cycle start press to continue with the W axis homing routine. That is easy to do. If I were doing this for a customer, I certainly would home at the bottom of travel. I generally have the knee in the top 1/4 of it's travel and being 1500+ pounds the knee and table, it does not move very fast, so homing will be quicker. But yes, you make a good point and it is one that I have considered, but my choice is based on the way I use the machine even though that may not be a good thing for a future user, but it is easy enough to disable the homing and switch, then just home the knee where it sits.
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