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Hi, Here I have added 2 options for connecting encoder on shaft. Motor, gearhead and shaft is connected using coupling. But where will be best place for encoder (To avoid backlash from coupling and gearhead). whether through hollow encoder is available? (see option 1). I dont know which one will be best for this kind of system. Which one is widely using arrangements?

Options 3 is Encoder will be placed before the motor.

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Most gear motors with integrated encoders have them placed on the motor shaft, which allows for much finer angle resolution at the output but does not account for backlash. I think this is what you mean by option 3.

Both options 1 and 2 are basically the same thing, with the only difference being that option 2 will account for any elasticity (twisting) in the shaft. Backlash will be measured with both options 1 and 2, since you are measuring the actual angle of the shaft. However, with option 3 you will be measuring the motor shaft angle and therefore need to multiply by the gear ratio to get the output angle -- plus backlash and elasticity will not be measured.

Also, yes you can get hollow shaft encoders, such as this one.

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  • $\begingroup$ Another item to consider is that, in the title, OP states the encoder is an absolute encoder. So, depending on the gear ratio, the required number of turns that the output shaft needs to make, and the type of absolute encoder, it may not be possible to use location 3. $\endgroup$
    – SteveO
    Commented Nov 20, 2015 at 0:28
  • $\begingroup$ Why do you say that? That just means you (might) have the encoder turning over multiple times per shaft revolution -- doesn't mean you can't keep track of that in the same code where you are applying the gear ratio. $\endgroup$
    – Brian Lynch
    Commented Nov 20, 2015 at 0:46
  • $\begingroup$ Sure, if you have an infinite-turn absolute encoder. But there are also multi-turn absolute encoders with a specific number of turns they can achieve. Depending on the application they can simplify the control because you don't need to keep track of turns in nonvol memory. I just want to make sure the poster doesn't get a bad surprise if that is the type of encoder for this implementation. $\endgroup$
    – SteveO
    Commented Nov 20, 2015 at 0:49
  • $\begingroup$ I wasn't aware there are encoders that cannot continuously turn. There are multi-turn and single-turn encoders but they don't usually have physical limits preventing them from turning continuously. $\endgroup$
    – Brian Lynch
    Commented Nov 20, 2015 at 0:55
  • $\begingroup$ Well the ones with limited turns are nice because, once calibrated, you never need to home the motor. On power-up you just read the absolute position. Here is an AB one with up to 8k turns: ab.rockwellautomation.com/Motion-Control/… $\endgroup$
    – SteveO
    Commented Nov 20, 2015 at 0:58

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