JVL MAC050 User Manual page 72

2.12 Absolute Multiturn Encoder
2.12.9 Extended encoder operation - endless relative moves.
In some applications the motor keeps moving in one direction with a certain length per
move.
Since the position counter have a limited working range this kind of operation will sooner
or later cause an overflow/wrap around situation.
To avoid the overflow/wrap around situation the actual motor position can be offset via
a command. This offset can be done at any time without losing any position information.
This feature is very helpful since the position counter will stay inside the working range.
Follow this setup sequence for doing a relative position offset:
1. To specify the offset distance write the desired offset distance (counts) to register 4
(P_NEW).
2. To actually offset the position value, one of the following actions can be done
- Write 248 to register 211 (COMMAND) or alternatively...
- Set bits 6 land 8 in register 36 (CNTRL_BITS) without changing the other bits.
This will add the value given in point 1 above to both the actual position and the target
position.
To actually perform a relative movement, there are two safe options and one not so safe/
precise.
Option 1, relative moves using P_SOLL.
1. Prepare for relative movement using register 3 (P_SOLL) by executing FastMac com-
mand 117 (96+21). This only has to be done once after start up. It selects what will
happen when a position register, one of P1 through P8, is activated by a FastMac
command.
2. Prepare the relative distance to move by writing it to one of the general purpose P1
through P8 position registers.
3. Execute a FastMac command that 'activates' the Px register. See the section for your
specific MAC00-xx interface module on how to execute FastMac commands.
This type of relative movement will set P_SOLL (target position)= P_IST (actual posi-
tion)+ Px in a safe way that avoids the type of error described in option 3 below. Note
that P_SOLL and P_IST will sooner or later exceed the operating range if this method is
used repeatedly, so you will need to use the relative position offset method described for
the absolute encoder in Extended Encoder operation.
Option 2, relative moves using P_FNC.
1. Prepare for relative movements using P_FNC by executing FastMac command 118
(96+22). This only has to be done once after start up. It selects what will happen
when a position register, one of P1 through P8, is activated by a FastMac command.
2. Prepare the relative distance to move by writing it to one of the general purpose P1
through P8 position registers.
3. Execute a FastMac command that 'activates' the Px register. See the section for your
specific MAC00-xx interface module on how to execute FastMac commands.
This type of relative movement will not change P_SOLL, so no wrap-around handling is
needed.
68 JVL A/S - User Manual - Integrated Servo Motors MAC050 - 4500
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