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Author Topic: Lagun knee mill with scales build using DSPMC  (Read 11879 times)

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Lagun knee mill with scales build using DSPMC
« on: November 10, 2011, 03:15:12 PM »
I have just recently started a retrofit control for an older anilam crusader M system that was on an Lagun FTV2 knee mill. It’s a larger machine that is in good shape mechanically with great looking ways and ball screws and has always been very accurate ( motor flange interpolated bosses and pockets easily within .001) but the controller was getting pretty flakey. It would go to snow on the screen from time to time and require a re-boot, sometimes more, to get going and this started getting more frequent. I tried many of the fixes I have read about for this issue ( battery, re-seating the boards and even chips, etc) but nothing seemed to do the trick. So, out it came! I have seen this on the horizon for a while and have been doing much research on a solid and viable solution for the last couple of years and finally settled on the DSP/MC-M (7762M) from Vital systems and Mach 3. I needed to have closed loop for the servos and this looks like the most reliable and versatile unit for this and several upcoming machines.

While I have done a new cnc control system before ( local group in Seattle – Actek) , I have never used Mach or this controller. I have gone through the manuals for both and while I am sure I will sort things out as I start getting things talking to each other, there are some hazy spots where I am not sure which is looking for what. I am using this project as a learning curve/test bed for several very large stone working bridge saws/machining systems that have much more complexity that this does. So, as I go through this you might see some ridiculous or over the top issues or requests which look strange for a knee mill, but this is so I can get some practice on something that won’t destroy itself or a multi-ton art piece if I screw something up.

Right now I am working on the E-Stop contactor and the main power runs. In the attached ( if I can attach it) drawing, I am latching the relay with the reset switch which is making the E-Stop contact closed to the DSP/MC through the 7535 board. Once configured within Mach is this all I need to do? Does Mach output an E-stop signal that would need to dump this relay? Does the DSP/MC trigger any sort of an E-stop signal say in case of a loss of communication with Mach or the PC?

In another bit of a twist, the machine is running glass scales. The motors have tach’s on them, but from what I have read these are now not used? In the original configuration they were routed directly back to the old drives ( ServoDynamics/Fenner). The question now is can I use the scales as the only feedback to the DSP/MC? I seem to recall reading this is possible but may require some more time spent tuning the motors to avoid excess hunting or over-shooting. Anyone have experience or suggestions on this?

Thanks much.



Re: Lagun knee mill with scales build using DSPMC
« Reply #1 on: November 13, 2011, 01:48:46 PM »
Welcome to the Mach3 forum j_boyss:

The dspmc controller is an excellent unit, and provides very solid control to servo motors.

I have one working for about a year and a half, and it has never given me a problem.

My servos are DC brush, .75 KW, with tach feedback, and 2000 line differential encoders. The motor tuning software has a visual graphic indication of the accel/decel curve, and motor response. The settings can be easily altered, and tested in real time, to achieve the best response for each motor/axis.

Why you wish to remove the tach feedback is unclear. A servo amp designed with a tach feedback will be inoperable (I believe) if the tach signal is deleted from the system. However, I do not claim to be an expert on all the servo/amplifier systems out there.

Linear scales or differential encoders are the digital "position" feedback to the system, not a part of the analog "velocity/acceleration" feedback, which the tach provides.

Mach3 does not "output" an E-Stop signal. Mach reads whether the physical E-Stop output signal is open/closed, hi/lo. The E-Stop signal is wired into the 7535 board, and correspondingly indicated in the "Inputs" section of the Ports and Pins configuration, i.e., pin#, active hi or lo. The E-Stop is a mechanical "Emergency stop."

You might read up on the "Reference" switches for setting the machine "Zero" coordinates. These are activated at the machine home limits. After these machine coordinates are set, then the "Work" zero position may be set, which can be saved in the Work table offsets.

The dspmc can utilize the encoder "Z" index channel for the machine coordinate reference position, which gives a very repeatable machine Zero if the encoder is driven direct to the leadscrew. I do not know if the glass scales incorporate a settable "Reference" point.

There are quite a few required settings in total, but just take them one at a time, and pretty soon it will all make sense. Get one axis working, and then proceed to the next.

Re: Lagun knee mill with scales build using DSPMC
« Reply #2 on: November 17, 2011, 05:26:44 PM »
Thanks for the response mrprecise44. Glad to hear a relatively long lasting success with this controller.

For the Tach question, I have no reason to omit these signals to the drives, I was just wondering if the DSPMC or Mach was looking for this as well.

I still am not sure if my scales ( anilam A-10 ) have this reference mark or not, I guess I'll just have to wait till its all hooked up and see.

On the Reference switches...Does the machine actually need to move to a home or a limit or a index pulse to be able to zero an axis? I never need to know this position as all my work is either a one-off or I locate off a fixed edge. I really hope I can just power things up and zero all the axis when I dial in my 0,0.

For tuning your motors, did you leave them coupled to the screws or remove them? In tuning things in the past it makes a lot of difference if the load changes much, at least from what I have seen.

Thanks again.

Re: Lagun knee mill with scales build using DSPMC
« Reply #3 on: November 18, 2011, 02:06:09 PM »
Hello j_boyss:

Regarding the tach signal, neither Mach or the dspmc controller incorporate it into their operation.

The tach signal is a feedback to the motor amplifier (or drive); it is integral to the function of the amplifier control of the motor. The amplifier receives the +/- 10v signal from the dspmc controller, and turns on the appropriate power diodes for direction, and motor velocity.

The response of the motor is known to the dspmc controller, as it is monitoring the encoder signals, the "A" channel being one direction, and the "B" channel being the opposite direction; the total amount of travel of an axis, from point (A) to point(B) is a known number of encoder counts by definition (it knows how many encoder counts per inch or mm) , and also supplying the +/- voltage signal.

The dspmc controller then applies the correct signal to accelerate and then decelerate (known as an S curve) to that position, at the commanded speed, which originated from the program in Mach. The dspmc does all this calculation according to the motor tuning parameters which have been input into the motor tuning PID (Proportional - Integral - Derivative: see Wiki) program.

When you tune the motors, each axis has a separate screen in the tuning section. You can see this S curve on the screen, and make changes in the PID settings for the best response. This capability of the dspmc is one of its strong points, regarding motor control. The actual internal actions in the controller are very complex, but the program makes the entire process very simple.
The tuning parameters are saved, and will be used from there on, at every start-up.

The dspmc controller is a "remote device" from Mach. It stores in a buffer, the incoming Mach3 X,Y,Z.... signals. Although they (Mach3 and the dspmc) work together, they are separate entities, that basically "talk to each other."

Regarding your question about the motors and the leadscrew:
As per above, the motor tuning involves the actual work involved to accelerate the weight of a machine table. The tuning is one of the final tasks to do, before using the machine.

Reference switches:
Some users do not use the reference capability. However, I personally believe it is a fundamental part of a CNC machine control.

If you use a "Z" index channel for setting the "Machine Zero", you can return to a known fixture position or setup position, without having to re-indicate a fixture. The reference switches are at the table travel limit. Usually at the machine's extreme + X, +Y, and +Z.

By using the encoder "Z" channel, the accuracy and repeatability of the resultant "Machine Zero" is as accurate as the encoder itself.

Conversely, if you use micro switches alone for the "Machine reference zero", your position is only as accurate as the mechanical repeat accuracy of the switch, which is not comparable to the digital encoder.

Another value to having a "Machine Zero" reference, is you can set your table "safe zones", a physical limit set in the ports and pins setup, with a given distance beyond which the program will not go. This will prevent the machine from tripping the limit switches, as it will not travel beyond whatever you set as that point in X,Y,or Z.

The "Work" zero positions are the G54, G55.....etc, which are referenced from the "Machine Zero".

If you have "reference" switches for X,Y,Z, you do a "Ref All" at a cold start-up. The machine moves in sequence through each axis, and automatically sets the machine "Zero". You then can click on "Go to Zero", and the machine will move to whatever work position is curently set, i.e. G54, G55, G56...... etc.

This process is automatic, and takes less than a minute. It is far quicker than using an edge finder to locate X, and Y, then having to put in a specific tool to re-set the machine "Z" home.

On a cold start, Mach does not know where it is (as in a known digital position) in relationship to the physical machine. All commercial CNC machines use a "Machine Zero" reference position.
 
Hope this is helpful