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Thread: Encoder for stepper motor

  1. #25
    Gold Member TomKerekes's Avatar
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    Default Re: Encoder for stepper motor

    Hi ssjantonio,

    The voltages seem safe to connect directly to 3.3V inputs as expected. 2.4V seems a bit low. Is that connected to KFLOP JP4 with the 150ohm termination? 8 of 10 of the I/O on JP4 have the termination. What pin is Z connecting to?

    Its difficult to check Z with a voltmeter because any pulse will be very short. That is why you seem to always observe the negative state.

    Konnect isn't a good choice for Index pulses because it is slower and requires higher voltage.

    It seems you have noise. You won't usually see narrow noise glitches on the Digital IO Screen because the sampling rate is relatively slow.

    Encoders should not normally be connected to earth GND at all. There should be a clean DC GND connection from KFLOP to the Encoder GND. Ideally it should also be shielded with the shield connected to the clean KFLOP DC GND on the KFLOP end only.

    HTH
    Regards

    TK
    http://dynomotion.com


  2. #26
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    Default Re: Encoder for stepper motor

    Thank you so much, you are right, the problem is the noise, I have connected a oscilocope to the A and Z phase in the encoder, I have attached the image. The machine is connected in a warehouse that has almost 50vfd drivers. How do you think that it can be solved?, all the drivers are connected to earth ground. I have isolated the machine and the encoders from earth ground.
    Maybe a EMI filter can solve the problem?Encoder for stepper motor-sin-t-tulo-png



  3. #27
    Gold Member TomKerekes's Avatar
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    Default Re: Encoder for stepper motor

    Hi ssjantonio,

    An EMI filter may help.

    Why are the signals at different levels ~ 0V and ~0.4V? Or are you using 10X Probes and that is really 5V per grid?

    Since you have a scope you should be able to see the index pulse if you trigger on it.

    Is KFLOP Isolated from earth GND?

    Are the cables shielded?

    How are things wired?

    Regards

    TK
    http://dynomotion.com


  4. #28
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    Default Re: Encoder for stepper motor

    Edit: yes the probe is 1:10 , and it was not configured in the software. I make a mistake. It looks closer to 0.4v displaced because it was at +5v, I'm sorry!. I will to take a new picture tomorrow.

    Hi tom, Kflop is counting correctly the pulses of the encoder, and yes, I can see the index pulse of Z, but it looks terribly noisly, I will try tomorrow to take a picture of the pulse.
    Yes, KFLOP is isolated from the earth GND, but the "GND holes" of kflop are disconnected from everthing. I have checked that all the electronics was isolated from earth ground. Only the power supply are connected to earth.
    The cables are shielded, but the shield is not connected.
    I have attached some pictures of the instalation. I have disconnected all the pumps, motors, valves, lamps, etc, and also I have changed the ATX supply, that is why it looks not wired.
    I have also tested connecting the power supply to a pc regulator, and the noise is still present.
    I really appreciated a lot your help, because I'm lost :S

    Encoder for stepper motor-20161027_194745_resized-jpg
    Encoder for stepper motor-20161027_194803_resized-jpg
    Encoder for stepper motor-20161027_194827_resized-jpg
    Encoder for stepper motor-20161027_194911_resized-jpg

    Last edited by ssjantonio; 10-27-2016 at 11:50 PM.


  5. #29
    Gold Member TomKerekes's Avatar
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    Default Re: Encoder for stepper motor

    Hi ssjantonio,

    Are you feeding in the signals into that 2 foot long ribbon cable dangling down?

    An ATX power supply normally has an internal connection from DC GND to Earth GND. I'd suggest getting a separate isolated regulated 5V supply. Probably 15W would be enough and are very low cost.

    The long and looped encoder cable is probably not helping.

    The Shield should be connected on the KFLOP end to KFLOP DC GND.

    The mounting holes for KFLOP are not electrically connected to anything.

    Regards

    TK
    http://dynomotion.com


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    Default Re: Encoder for stepper motor

    Hi Tom, I have followed your recommendations:
    I have an isolated 5V power supply for the encoders only.
    KFLOP is connected to the ATX power supply (the noise at the output of the ATX is negligible 147mA max).
    The long and looped encoder cable has been cut off.
    The shield is connected to the GND of the 5V power supply instead of KFLOP (The blue cable of the encoder is connected also to the shield of the encoder and the shielded cable), because I was affraid to danger the KFlop board. (If I connect the shield to earth ground insted of the DC GND the noise is reduced almost 30%)
    I have used a new shorter cable (4inches) for input JP4.

    I have attached two pictures:
    The first is with the osciloscope connected directly to the output of the encoder.
    The second one is connected directly to the input to KFlop (is still disconnected because I'm not sure if the voltaje peaks cause a damage to the board).
    If I connect the Z phase to Konnect, it works perfectly, but only at low feed speed.

    Encoder for stepper motor-sin-t-tulo-png
    Encoder for stepper motor-sin-t-tulo2-png

    With this configuration it works on konnect, but like you say it is not good because the low voltaje, I have noticed that at high speeds it does not detect the pulse.

    There is a posibility to use an active rc filter before the connection to kflop? Or what else can we do to reduce the noise?

    Thank you again!



  7. #31
    Gold Member TomKerekes's Avatar
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    Default Re: Encoder for stepper motor

    Hi ssjantonio,

    I have an isolated 5V power supply for the encoders only.
    The encoders require a common GND to KFLOP. So the encoders will not be isolated from KFLOP. I guess by isolated you are referring to isolated from Earth GND?

    KFLOP is connected to the ATX power supply (the noise at the output of the ATX is negligible 147mA max).
    Like I said before ATX power supplies have an undesirable Earth GND connection. So you shouldn't use them if possible. I assume you mean 147mV?

    Is your scope isolated? If not connecting the scope will make a GND connection and change things.

    The long and looped encoder cable has been cut off.
    Good

    The shield is connected to the GND of the 5V power supply instead of KFLOP (The blue cable of the encoder is connected also to the shield of the encoder and the shielded cable), because I was affraid to danger the KFlop board. (If I connect the shield to earth ground insted of the DC GND the noise is reduced almost 30%)
    You should be able to connect the shield to KFLOP GND without any Danger of damaging KFLOP (if the shield is isolated from everything else).

    The second one is connected directly to the input to KFlop (is still disconnected because I'm not sure if the voltaje peaks cause a damage to the board).
    I don't understand. You state it is wired to KFLOP and then say it is not wired to KFLOP?

    What input pin are you using?

    If I connect the Z phase to Konnect, it works perfectly, but only at low feed speed.
    Do not use Konnect

    Measure the pulse time at your highest RPM.

    An RC filter would be a good idea. Assume Tau = 5us = RC. Assuming R=100 ohms:

    C = 5us / 100ohms = .05uF

    Regards

    TK
    http://dynomotion.com


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    Default Re: Encoder for stepper motor

    To avoid mistakes, I have attached a diagram showing my wiring. The Earth ground is isolated from everthing. I'm sorry for my bad picture jeje I'm just a chemical engineering having fun con Kflop .
    Encoder for stepper motor-pieza13-jpg



  9. #33
    Gold Member TomKerekes's Avatar
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    Default Re: Encoder for stepper motor

    Hi ssjantonio,

    A picture is worth a thousand words

    KFLOP doesn't need 12V and the way you have it connected with no GND would mean the power supply wouldn't do anything.

    So it seems you changed from using an ATX supply?

    You have not connected the encoder index signal?

    Regards

    TK
    http://dynomotion.com


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    Default Re: Encoder for stepper motor

    Hi Tom,
    Yes I Have changed the ATX, I'm using 12V for Inductive sensors. I have tested and yes, with that wiring the sensors does not work . I will to connect them directly to the 12V.
    If I connect the encoder index signal to IO16 with a 47ohm resistence, the function ReadBit always returns HIGH. I have tested with a clean 3.3V from KFLOP to IO16 and the ReadBit works fine.

    Thank you!



  11. #35
    Gold Member TomKerekes's Avatar
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    Default Re: Encoder for stepper motor

    Hi ssjantonio,

    If I connect the encoder index signal to IO16 with a 47ohm resistence, the function ReadBit always returns HIGH. I have tested with a clean 3.3V from KFLOP to IO16 and the ReadBit works fine.
    I don't understand what you are saying. Do you mean it is always low? What is the voltage level of the encoder index signal before connecting it? After connecting it? Scope the KFLOP Input pin to see the pulse. Determine the voltage level and pulse length.

    IO16 has a 150 ohm pull down resistor. The encoder signal may not have enough output current to drive that heavy of a load load. You might use IO24 or IO25 which do not have the pull down resistors.

    Regards

    TK
    http://dynomotion.com


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    Default

    Quote Originally Posted by TomKerekes View Post
    Hi ssjantonio,

    I don't understand what you are saying. Do you mean it is always low? What is the voltage level of the encoder index signal before connecting it? After connecting it? Scope the KFLOP Input pin to see the pulse. Determine the voltage level and pulse length.

    IO16 has a 150 ohm pull down resistor. The encoder signal may not have enough output current to drive that heavy of a load load. You might use IO24 or IO25 which do not have the pull down resistors.

    Regards
    Edit: it was working, but now the function ReadBit(24) always return true. And I cant see any peak in the osciloscope. The pulse mas frequency is 6.95khz and the pulse duration 144uS.

    I have tested in IO24 and it work perfectly. But there is only two available ports and I have 5 encoders. If I using only for homing, can I connect all of them in a single IO?

    Last edited by ssjantonio; 11-02-2016 at 10:05 PM.


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