Help - how do I tear down a Siemens 1HU3056 DC servo?
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  1. #1
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    Default Help - how do I tear down a Siemens 1HU3056 DC servo?

    Looking in thru the brush holder with the brushes removed I can see that the commutator needs some attention. I have removed the 4 nuts on the main body bolts and the 4 screws thru the nose casting that pull in the front bearing retainer and then removed the front nose casting from the motor body. I have also removed the rear cover and the rear casting with the position sensor mounted in it. The main motor housing with the field pieces has been slid off of the armature. Finally, I removed the ring that holds the tach generator brushes. The armature and brush housing and the tach generator are now out and on the bench as an assembly.

    The armature is still held firmly in position in the brush housing casting. It spins freely in the bearing but it does not move axially. Either the rear bearing is pressed onto the armature and retained in the housing by a press into the housing, or the tachometer generator is retained on the rear end of the armature shaft preventing the armature from being pulled out of the brush housing. Clearly the motor tachometer rotor is too large to slide thru any armature bearing and clearly it must be removed before the motor can be disassembled further.

    So, how is the tach generator retained on the armature shaft and how do I remove it?

    There is a hex on the rear of the armature shaft. Is this hex a feature machined into the armature shaft itself and not removable, or is it a second part that can be unscrewed from the armature shaft? If so does this part retain teh tach generator?

    The ID of the tach generator appears to be larger than the hex on the rear of the armature shaft. Does the tach generator simply slide over the hex and press onto the armature shaft? If so, how do I get a hold on it to pull it back off the armature shaft? Do I simply press on the shaft end while holding the brush casting against the press force? What is the acceptable process to remove the tach generator?

    Once the tach generator is removed, does the brush housing simply slide off the armature or do I have to pull that apart too? Will the rear bearing be damaged in the process and need to be replaced?

    When I get it all apart, I will turn the commutator and reassemble these parts. Any advice on tool geometry for turning the commutator?

    Then I want to install an electric brake in between the tach generator and the position encoder and make a new rear shaft extension for driving the brake and the position sensor.

    Out of curiosity, is there some special fixture used to hold the motor body (field section) while pulling the armature from the main motor field housing that keeps the armature centered in the field pole pieces and prevents the armature from making contact with the field poles? If they make contact is the motor demagnetized and ruined.



    All help appreciated.

    siemens-servo-disassembly-021.jpg

    siemens-servo-disassembly-019.jpg

    siemens-servo-disassembly-020.jpg

  2. #2
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    That commutator looks pretty good. Why are you risking damage to the motor to give it "attention"?

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    "That commutator" that is exposed and visible in these photos is part of the servo tachometer generator - not part of the motor itself. It is a low voltage and low current commutator and unlikely to be damaged. So yes - it is in good condition and it does not need attention. The rotor immediately behind the commutator is also part of the tach generator and is the part that must be removed to pull the main motor armature out of the brush holder casting.

    The main motor commutator is up inside the brush holder casting and is not visible in the photos. It can be seen if you look down thru the empty brush holder. It has one bar that is pitted and visibly burned. I am concerned that motor operation will be erratic when this particular commutator bar is under the brush and is in action. Turning the commutator requires pulling the armature out of the brush holder casting - thus the question.

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    Ok. I thought you had it further apart than that.

    I asked a friend who does this kind of thing and he said that the tachometer is taper fit to the rotor shaft. I asked him how to remove it and he said "very carefully" and sent me this picture:

    2017-07-07-08.18.04.jpg

    It looks like you're going to have to make some kind of expanding puller thing to get between the rotor shaft and the resolver shaft.

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  6. #5
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    Thank you for your efforts in getting informatin for me. The information helps.
    If you could possibly ask you friend for some details:

    1) Is the tach fitted directly onto a male taper on the rotor shaft end or is it on its own extension shaft that then goes on or into the taper on the rotor shaft end?

    2) If the tach is on an extension shaft is the rotor shaft end a male taper or a female taper socket?

    3) Is the rotor shaft threaded for a retention screw that holds the tach assembly onto the rotor shaft end, or is it just a self locking friction grip type taper?

    My tach seems to be pressed on a shaft (main or extension is unknown currently) that is threaded internally for a screw. It has a shaft extension screwed into it that drives the position sensor. It is not clear if:

    1)this is for a jack screw put there for removing the tach generator.
    2) this is for a retention screw to clock the tach generator onto the rotor shaft.
    3) this is a provision to allow screwing in an extension shaft for other accessories like a position sensor.

    Any details would be greatly appreciated as I do not want to ruin this motor.

  7. #6
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    Well, it is apart.

    The tachometer generator is retained on a separate piece of shat that is joined to the main motor shaft via a taper socket on the motor shaft and a male taper (very similar to a Jacobs taper) on the tachometer shaft. The motor shaft has a small threaded hole and a screw passes thru the tachometer shaft and threads into the hole in the motor shaft retaining the tach shaft. On this motor that screw was missing. The tachometer shaft itself has a slightly larger drilled and threaded hole. A pin can be inserted into these holes and then a bolt can be screwed in and used as a jacking device to remove the tachometer shaft from the motor shaft. Once the tachometer is off, the rotor can be slid out of the brush holder casting.

    Problem was, like Jacobs taper drill chucks that seem to get almost welded on, the tachometer shaft was really really stuck on the motor shaft to the point that I questioned whether or not the tach really was on a separate removable shaft. There are only about 3 threads inside the tach shaft that engage the jack bolt. I am really surprised they did not strip given how hard I had to torque the jack bolt. And yes, I did fill the hole with Kroil penetrant and let it stand over night before I started.

  8. #7
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    I know Old post but anyhow
    Just loosen or remove the bolt Clamp the shaft in a vice Put a ringspanner on the hex and turn it loose
    Eighter direction will do
    I would store the tach assembled



    Peter


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