Technical Newsletter # 1
Welcome to the 1st edition of "JVL Tech News". The technical newsletter is a newsletter that contains more technical details and informations than JVL news. If there's any updates on firmware/software or new features, you can keep updated in this newsletter.
1. Absolute Encoder 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 MAC 400/800 the Absolute Encoder is partly mechanical (tooth wheels) so no backup battery is needed.
The encoder is multiturn and has up to ±1024 Revs.
Single turn Resolution in MAC 800 = 8000 CPRSingle turn Resolution in MAC 400 = 8192 CPR (default, can be changed to 8000 CPR)
I.e. the resolution is the same as for the incremental encoder (where again MAC 400 can be set to 2000 or 2048 PPR = 8000 / 8192 CPR).
Two registers are used for the Absolute Multiturn Encoder in MAC 400 and 800:
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.
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 MAC 400 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:
2. Synchronize Position Registers Inside an RxP Program
(ONLY Incremental Encoder), module MAC00-R1/3/4
If you want to change the Actual position to a new value, e.g. to move the Home position, also the Requested position and some internal counter registers have to be changed or synchronized as well.
This is also useful when changing modes, e.g. from Velocity to Position mode. Here is how to do it:
1) First make sure the motor is at a standstill (so Actual and Requested position don’t change while performing the sync), e.g.:
(2B) In MAC 400…800 you use lines like the following – using the value for Sync Position that you want (as shown 0 or Actual position – or another value):
(Control bits: Manual Resync = Bit 10 ON in MiniMAC / Bit 6 ON in BigMAC).
JVL Industri Elektronik A/S, Blokken 42 , 3460 Birkerød, Denmark
Tel: +45 4582 4440. E-mail: jvl@jvl.dk. Web: www.jvl.dk
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