MAHO 1000 c hardware with Kanalog KFlop controller advice

[salvador12]

The original servo motors have only built in tachogenerators with feedback back to the original drive amplifiers. nothing more.

[TomKerekes]

The original servo motors have only built in tachogenerators with feedback back to the original drive amplifiers. nothing more.

That's good. Some feedback from the motor shafts is usually required to have a stable system with linear scale feedback.

[salvador12]

but if i put rotary incremental encoders on the servo motors then I have no linear scales , could I just do with those rotary encoders or should I instead put linear scales?

[TomKerekes]

but if i put rotary incremental encoders on the servo motors then I have no linear scales , could I just do with those rotary encoders or should I instead put linear scales?

Linear Scales are almost always preferred as they have the big advantage that more mechanical errors can be corrected. Because the actual table position is being measured, and is known, the servo will keep making adjustments until the table is at the desired position. Things like lead screw errors, backlash, compliances, etc. can be potentially eliminated. With only rotary encoders the Servo can position the motor/leadscrew correctly, but any mechanical errors between that and the table will remain uncorrected.

Note however that even though the feedback loop will attempt to correct these errors they will not necessarily be completely eliminated. How large the errors will be is dependent on the dynamics of the system. The dynamics will determine how quickly corrections can be made.

One disadvantage with Linear Scales is that because more mechanical issues are in the feedback loop it can be less stable and more difficult to tune. This is why velocity feedback from the motor shafts is useful. Otherwise controlled motion of the motors can be difficult. For example when moving through backlash the Linear Scales don't provide any information at all.

So in summary, I'd suggest adding new Linear Scales and keep the tachometer feedback to your amplifiers.

[RotarySMP]

Oh right. The Indramat closes the velocity control loop, with the tachos, while the control (Phillips432, or in my case LinuxCNC through MESA 7i77) closes the position loop with the linear encoders. If you rip out the Indramat, you are missing the velocity control loop.

[TomKerekes]

Yes I would keep the existing drives and power supplies if possible. Here is a simple test to check that you have found where to inject the +/-10V Velocity command as well as have them powered and enabled.

There are many other "dumb" drives that allow tachometer feedback to control velocity. a-m-c.com is one source.

HTH

[salvador12]

Well ofcourse I am keeping the tacho feedback to the drive amplifiers, otherwise my servo motors would not work.
Yes I am keeping the original indramat drives and servo motors and they all work by inputing a differential voltage of +-10 volts so I can just connect them to the respective kanalog output pins.

I guess at first I will set up incremental rotary encoders on each of the servos since the original linear scales will not be working with the Kanalog, if the accuracy wont be good enough then I will also buy new linear scales so that each axis will then have both a rotary as well as a linear scale.

Now since the shafts are good enough , what incremental rotary encoders would you suggest, what would be the maximum pulse rate I should be looking for because I suppose the Kanalog and Kflop has a maximum resolution that it can take in above which there is no use to go.


PS. is it normal that when the servo motors are enabled (the thyristor drive signal is applied to the input in the amplifier) that when I decrease the differential input voltage to zero which corresponds to a standstill of the motor the motor itself is humming sort of like vibrating , the motor is standing still and actually it's rotor ir almost feels like magnetically locked yet it's humming, now since a DC permanent magnet servo motor is just well a DC brushed motor, what is happening in this moment? Is it okay for it to be like that because normally motors get overheated and burn down when stalled etc, I suppose the amplifier is sending some sort of a anti phase voltage to the motor or what is exactly happening here can you explain?

each servo motor also has a brake but i suppose the brake is not used whenever the motor simply is stopped in a waiting position for each axis right?

[TomKerekes]

Now since the shafts are good enough , what incremental rotary encoders would you suggest, what would be the maximum pulse rate I should be looking for because I suppose the Kanalog and Kflop has a maximum resolution that it can take in above which there is no use to go.

KFLOP/Kanalog conservatively accept up to 1 million quadrature counts/second. So for example if the max RPM of the encoder is 3000RPM then the maximum encoder resolution will be:

1e6 / (3000/60) = 20,000 counts/rev or 5000 lines or cycles per rev.

PS. is it normal that when the servo motors are enabled (the thyristor drive signal is applied to the input in the amplifier) that when I decrease the differential input voltage to zero which corresponds to a standstill of the motor the motor itself is humming sort of like vibrating

Its hard to say whether that is the Drive Switching or analog noise being picked up. I'm not familiar with those Drives but switching frequency is usually higher than a "hum". Usually > 10KHz. 60 cycle noise being picked up in the analog wiring either in the +/-10V input or the tachometer could cause a 60 or 120 Hz "hum". If you had KFLOP/Kanalog connected you could plot how much encoder motion is occurring and at what frequency. I doubt it would cause motor damage. Monitor the motor temperature.

the motor is standing still and actually it's rotor ir almost feels like magnetically locked

The velocity feedback (tachometer) will attempt to maintain zero velocity with a command of zero input. If the Velocity loop it working well it will be very hard to move the motor. When not trying to resist motion the motor current/torque should be very low.

each servo motor also has a brake but i suppose the brake is not used whenever the motor simply is stopped in a waiting position for each axis right?

Normally the brake is only used to avoid motion after a loss of power. Such as to stop the Z axis falling down.