Why two different battery locations for memory card backup power?

    Sorry in advance for a newbie question.


    I understand that robot position data is stored in a volatile memory card in a robot controller and that is why it needs a battery at power loss.


    Why does a typical industrial robot also have additional battery on the robot itself at the base?

    I thought that too but why would the encoders need backup power? When normal power is not there what good are the encoders? I mean, there has to be something that processes the encoder feedback, and that would need power. Encoder signals wouldn't go straight into the memory card, right? Thanks for your reply.

    There are many variations of encoders that are used on Robotic Systems, most use hybrid types:
    - Absolute
    - Incremental


    Simple explanations can be found on the net like the following: https://www.posital.com/en/pro…solute-vs-incremental.php

    When power is removed, and reapplied, then yes, it is safe to assume the absolute position should be saved by the controller........but what about the encoder?
    - Feedback to the Controller is by use of communication protocols, this equates to the encoder being an intelligent device - ie control electronics = power required to function.
    - All of the signals are therefore contained in the 'data' being transmitted from the encoder....so the encoder requires power for this....without power = loss of data/loss of position.


    What happens if you rotated the encoder (moved the arm) without power and no battery for the encoder.
    - The physical relationship between encoder position and encoder value would be out of sync....so how could the controller know by how far, how many rotations, and what direction?
    - By having the encoder powered at all times.


    Hope this helps..........

    Not all robots use this. Different brands do it differently.


    For those robots that [b]do[b] require batteries in the base of the arm, this is usually because there is some volatile memory storage on a circuit board in the arm. Usually, this is in place to preserve the "zero" setting of each resolver/encoder, which is a unique property per axis per robot. For robots that store these critical offsets in volatile memory (like SRAM), a small power supply is necessary so that the memory is not lost whenever the control cabinet is shut down, or if the arm is disconnected from the cabinet. It is also valuable if, for any reason, one needs to swap a robot between different cabinets.


    Some robot brands use non-volatile memory to fulfill this function (EEPROM). Most KUKA robots function this way. One of the tradeoffs is that EEPROM can have a shorter lifespan, in read/write cycles, than a batter-backed SRAM.

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