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Thread: Absolute encoders

  1. #21
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    Default Re: Absolute encoders

    Quote Originally Posted by rick027 View Post
    Have to disagree with mactec54 on the absolutes, because I run a weeke 050 and a nester they both have absolute encoders and these machines know where they're positions are at all the time..
    No one said a machine with Absolute Encoders does not know where it is at all times, they do, the question was about machining Homing which can be control forced or just start from where ever your machine stopped it's your choice as long as the Absolute Battery is maintained which most CNC machines still have some are not using Battery's now which is all the more reason to Home your machine nothing is perfect as it should be

    Mactec54


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    Default Re: Absolute encoders

    Quote Originally Posted by rick027 View Post
    Jim my budget is about 1200
    This is what you want to be looking at DMM | Technology Solutions | AC SERVO DRIVE | AC SERVO MOTOR | ROTARY ENCODER $1200 would be a little light depending on what size motors you need

    Mactec54


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    Default Re: Absolute encoders

    Thanks Mactec54



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    Default Re: Absolute encoders

    for an understanding of absolute encoders and incremental encoders:

    https://en.wikipedia.org/wiki/Rotary_encoder
    https://www.posital.com/en/products/...ncremental.php

    hth



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    Default Re: Absolute encoders

    Hi,
    absolute encoders can tell exactly where they are within one rotation. Most CNC machines however require the stepper or servo turn many times,
    maybe one hundred or more revolutions from one end of travel to the other. An absolute encoder won't help that much.

    You may have been thinking about the very latest 'multi-turn absolute encoders'. They are still at this time a fairly rare breed, They will have 24 bit
    or more, wide positions with say 8 bits dedicated to the number of complete turns from 'home' and the remaining 16 bits describing the angular
    position within that one revolution. To my knowledge all of these encoders have a high speed serial interface.

    I think it unlikely that you will be readily able to get one of these devices and certainly not cheaply. Even if you do you will still have to build your
    own highspeed serial interface. Unless you are familiar with high speed electronic design I think its a bust.

    May I suggest that you look at servos that have that capacity built in. Delta (Taiwanese, made in China) A3 series have 24bit multiturn absolute
    encoders with battery backup. I believe also the DMM (Canadian, made in China) have models fitted with a 30bit multi-turn absolute.
    They are not widely advertised so an email may be required to secure more info.

    Craig



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    Default Re: Absolute encoders

    Quote Originally Posted by joeavaerage View Post
    Hi,
    absolute encoders can tell exactly where they are within one rotation. Most CNC machines however require the stepper or servo turn many times,
    maybe one hundred or more revolutions from one end of travel to the other. An absolute encoder won't help that much.

    You may have been thinking about the very latest 'multi-turn absolute encoders'. They are still at this time a fairly rare breed, They will have 24 bit
    or more, wide positions with say 8 bits dedicated to the number of complete turns from 'home' and the remaining 16 bits describing the angular
    position within that one revolution. To my knowledge all of these encoders have a high speed serial interface.

    I think it unlikely that you will be readily able to get one of these devices and certainly not cheaply. Even if you do you will still have to build your
    own highspeed serial interface. Unless you are familiar with high speed electronic design I think its a bust.

    May I suggest that you look at servos that have that capacity built in. Delta (Taiwanese, made in China) A3 series have 24bit multiturn absolute
    encoders with battery backup. I believe also the DMM (Canadian, made in China) have models fitted with a 30bit multi-turn absolute.
    They are not widely advertised so an email may be required to secure more info.

    Craig
    Actually multi-turn absolute encoders have been in quite wide use for more than 20 years ( By FANUC, YASKAWA, OKUMA etc)
    Older ones use battery backed-up electronic turn counters or geared turn counters. Some new ones from Broadcom and others use electronic
    counters powered a Wiegand effect generator so no backup battery is needed. Absolute encoders are almost a necessity in robotics and allow CNC machines
    to avoid homing at startup



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    Default Re: Absolute encoders

    The two links I included seem to imply an absolute encoder doesn't require power to maintain position knowledge. They both say an absolute encoder knows where it is at power up.
    If it requires power to maintain position knowledge it is an incremental encoder with battery backup no matter the type of data sent from the encoder to the control/drive. Convenient for many machines but for a robot it would be almost useless.



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    Default Re: Absolute encoders

    Quote Originally Posted by stustev View Post
    The two links I included seem to imply an absolute encoder doesn't require power to maintain position knowledge. They both say an absolute encoder knows where it is at power up.
    If it requires power to maintain position knowledge it is an incremental encoder with battery backup no matter the type of data sent from the encoder to the control/drive. Convenient for many machines but for a robot it would be almost useless.
    Single turn absolute encoders do not require power to maintain position (the position is read from the code wheel)

    Geared multi-turn absolute encoders do not require power to maintain the turn count but suffer from wear, noise etc

    Most current multi turn encoders (That FANUC uses extensively in their robots for example) use battery or super capacitor backup power to maintain the turn count

    Some very new multi-turn encoders use the Wiegand effect to harvest energy for writing their multi-turn memory so do not require batteries or super capacitors



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