Store Multiturn
The Store Multiturn saves multiturn counts from a feedback to memory and restores it on power cycle. Multiturn counts are the number of revolutions a feedback device
A process whereby some proportion of the output signal of a system is passed (fed back) to the input.
In automation, a device coupled to each motor to provide indication of the motor's shaft angle, for use in commutating the motor and controlling its speed and position has traveled in one direction. A feedback can have multiturn counts ranging from 0 (none) to 231 bits of multiturn count. A typical multiturn absolute feedback has 212 mutiturn counts.
It specifies the number of single turn-bits or power of 2 counts (range 22 to 232) to use to determine if the motor has moved. Kollmorgen recommendeds using as many bits as possible to make the machine safe.
There are several limitations because the drive saves multiturn counts.
Limitations
Store Multiturn requires an absolute feedback device that allows the drive to detect and fault if the motor moves while the power is off. It is dangerous for the motor to move while the power is off then the machine starts and is not in the correct position.
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- When changing feedbacks, turn the multiturn feature off and then back on to reset the stored position. It is possible to install a new feedback within the single-turn range as the previous feedback and the drive does not detect a change.
If the motor moves while drive is off, then the drive faults on power up and multiturn counts reset. For example, if a running machine stops due to a power outage then the drive faults on power up and the stored multiturn counts reset.
| Keyword | Description |
|---|---|
| FB#.STOREMULTITURN.ENABLE | Enables or disables the store multiturn feature. |
| FB#.STOREMULTITURN.BITS | Sets the number of single-turn bits used to determine if the position stored is valid after power cycle. |
AKD1G Keyword Equivalents
The two capture units are now called CAP1 and CAP2 instead of CAP0 and CAP1.
| AKD1G Keyword | AKD2G Equivalent |
|---|---|
| FB1.EXTENDEDMULTITURN | FB#.STOREMULTITURN.ENABLE |
Typical Uses of Store Multiturn
Store Multiturn can be used if the existing absolute feedback counts do not meet the travel required in one direction.
Example Configuring FB#.STORE.MULTITURN.BITS
The drive uses 264 counts for position. One bit, the sign bit, determines direction, 31 bits determine the number of revolutions (multiturn bits), and 32 bits are used to determine where you are in a revolution (single turn bits). If configured to use 2 bits, of the most significant single-turn counts, to determine if the motor has moved, then the motor could move up to 360 degrees/22 = 90 degrees while the drive is powered down. For some machines this may be minimal movement and for others this may be safe; therefore, it is configurable.
