FAQ
Absolute Encoders in MAC400/800 ?
|
Absolute Encoders
in MAC400/800. |
The big advantage of having an Absolute Encoder is that you only
need to reset the encoder value once, then you can drive and always
have a correct absolute encoder counter value - no matter how many
power cycles you make.
In other words the motor remembers it’s encoder counter value.
In MAC400/800 the Absolute Encoder is partly mechanical (tooth
wheels) so no backup battery is needed.
Important!
The encoder is multiturn and has up to ±1024 Revs.
Single turn Resolution in MAC800 = 8000 CPR
Single turn Resolution in MAC400 = 8192 CPR (default, can be
changed to 8000 CPR)
I.e. the resolution is the same as for the incremental encoder (where
again MAC400 can be set to 2000 or 2048 PPR = 8000 / 8192 CPR).
Two registers are used for the Absolute Multiturn Encoder in MAC400
and MAC800:
Reg 225: P_OFFSET
Used to adjust the zero position for absolute multi-turn encoders. Reg 226: P_MULTITURN
The full multi-turn position read directly from the absolute encoder (multiplied with -1 if the "Invert motor direction" bit is set to 1).
How to reset the encoder?
From MacTalk only: Move the MAC motor to the correct new 0 (zero) position, then first click the button [Reset position] — and then [Save in Flash].
Pressing [Reset position] will also prompt you to press [Save in flash]:
 If an RxP Program is running: First you have to STOP the RxP program — go to the "MAC00-RxP" tab and click the [Stop] button.
Then follow the instructions above ‘From MacTalk only’.
IMPORTANT
As the encoder has up to ±1024 Revs, you have to be careful to reset the encoder at a reasonable position.
Suppose the actual position corresponds to 1022 Revs and you perform a reset — then you can only drive 2 more revolutions before you will get an "overflow" in the counter.
When e.g. the MAC400 drives past (exceeds) +8.388.606 Cnt (1024 x 8192 = +8.388.608 Cnt), then the counter value in Reg 226 "wraps around" to the value -8.388.608 Cnt !
While driving it’s no problem to exceed 8.388.606 cnt, the motor keeps on driving in the desired direction and stops correctly — BUT after a power cycle Actual and Requested positions (P_IST and P_SOLL) are both set to the same absolute counter value:
P_IST = P_MULTITURN + P_OFFSET |
JVL A/S Bregnerødvej 127 DK-3460 Birkerød Denmark
Tel: +45 4582 4440 Fax: +45 4582 5550 E-mail: jvl@jvl.dk
Tel: +45 4582 4440 Fax: +45 4582 5550 E-mail: jvl@jvl.dk
