The original servo motors have only built in tachogenerators with feedback back to the original drive amplifiers. nothing more.
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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.Quote:
The original servo motors have only built in tachogenerators with feedback back to the original drive amplifiers. nothing more.
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.Quote:
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?
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.
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.
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
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?
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:Quote:
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.
1e6 / (3000/60) = 20,000 counts/rev or 5000 lines or cycles per rev.
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.Quote:
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 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.Quote:
the motor is standing still and actually it's rotor ir almost feels like magnetically locked
Normally the brake is only used to avoid motion after a loss of power. Such as to stop the Z axis falling down.Quote:
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?
So I guess the Kanalog inputs for each axis encoders are more than with enough reserve , my servo motors are DC permanent magnet motors and their max RPM is 1200, maybe you can already recommend a know and optimal price/performance encoder for me to buy because there are so many to choose from it would ge good to have some advice.
PS. so the Kanalog input for 1 million counts/sec is basically a 1 Mhz input ?
In other words unless my motor rotor would spin at a million RPM it gives a high enough resolution for very precise control at low RPM right?
As for my drives yes I believe they are working ok, at zero volts differential input the rotor is stopped and also locked in position as I can't move it by hand not a single bit.
The hum I believe is from the mains frequency which is supplied to the motor rotor through it's comutator from the drive amplifier in order to hold it in place. My drive amplifiers (Indramat TRM3) use a thyristor output controlled by thyristor control IC's , I looked through the schematics as well as the drives themselves and it seems so , so basically it takes the three phase input and uses the positive and negative half periods to move the motor in either one or other direction and then chops off the period at the necessary place in order to have RPM control, as far as I understand there is no switching of high frequency involved in this amplifier.
So I understand that the electric brake is supposed to be released only when the machine is turned off in order to lock the tables and axis in place right ? so when working the only thing that stops and holds each axis is the motor itself?
You could use https://ro.mouser.com/ProductDetail/...wXWth5sxgovg==
On my maho i had heidenhain Linear scales. But they were sin cos 10uA. But inside the old coltroller i found a dedicated board that convert the scale signal to TTL
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USDigital is a good source. You will need to select what will work for you mechanically. Most any digital incremental encoder should work. Choose a differential output as that can work with either single ended or differential encoder inputs. For more info see here.Quote:
my servo motors are DC permanent magnet motors and their max RPM is 1200, maybe you can already recommend a know and optimal price/performance encoder for me to buy because there are so many to choose from it would ge good to have some advice.
There is often confusion between encoder cycles/rev vs (quadrature) counts/rev. Each encoder line creates a complete quadrature cycle or 4 quadrature counts.Quote:
PS. so the Kanalog input for 1 million counts/sec is basically a 1 Mhz input ?
In other words unless my motor rotor would spin at a million RPM it gives a high enough resolution for very precise control at low RPM right?
KFLOP/Kanalog conservatively accepts up to 1 million quadrature counts per second, or 250KHz cycles/second.
With a maximum speed of 1200 RPM the maximum counts/rev in order to avoid exceeding 1 million counts/second would be:
1,000,000 / 1200 x 60 = 50,000 counts/rev (12,500 cycles/rev)
The higher the resolution the better velocity can be measured at low RPM.
That sounds good, except I would expect without any position feedback, and only velocity feedback, I would expect there to be some slow drift and manually applying torque would cause some slow movement. Are you sure the motor is really locked into a fixed position? Or just very resistant to movement? You might read this article in our wiki.Quote:
As for my drives yes I believe they are working ok, at zero volts differential input the rotor is stopped and also locked in position as I can't move it by hand not a single bit.
I think you are probably correct, except I think it works in reverse. The Thryister switches/latches on at some point during the 60Hz AC cycle and then conducts for the remaining portion of the cycle. So a 120Hz hum would be expected.Quote:
The hum I believe is from the mains frequency which is supplied to the motor rotor through it's comutator from the drive amplifier in order to hold it in place. My drive amplifiers (Indramat TRM3) use a thyristor output controlled by thyristor control IC's , I looked through the schematics as well as the drives themselves and it seems so , so basically it takes the three phase input and uses the positive and negative half periods to move the motor in either one or other direction and then chops off the period at the necessary place in order to have RPM control, as far as I understand there is no switching of high frequency involved in this amplifier.
YesQuote:
So I understand that the electric brake is supposed to be released only when the machine is turned off in order to lock the tables and axis in place right ? so when working the only thing that stops and holds each axis is the motor itself?