Position/Synchron Control Features; Position Calculation - ABB ACSM1 Manual

Position/synchron control features

Position calculation

The actual position of the drive is measured using a position feedback device.
During normal operation, the actual position is calculated by keeping track of the
position change between the current time and the last known position. The position
calculation is non-saturating: after the maximum position has been reached, the
position gets the negative value with the maximum absolute value.
Depending on the machinery used, different types of scaling can be applied to the
position measurement for drive position calculation, such as
• unit (parameter
• feed constant, transforming rotational axis movement to translational
FEED CONST
• gears
MUL,
• axis type
• resolution of the position calculation
The drive position system range is defined by
MINIMUM
MAX or POSITION ERROR MIN) is generated. The range is supervised in position,
synchron and profile velocity modes.
Hardware limits can be established by parameters
62.06 POS LIMIT
direction is ramped down along the emergency stop ramp, and only movement in the
opposite direction is allowed. In the homing operating mode, when seeking the home
position, the drive does not use the limit switches; they are however used in some
homing methods to reverse the direction of movement when seeking.
With an absolute type of position feedback, the actual position after a power-up or an
encoder refresh request is calculated on the basis of the measured number of
revolutions of the absolute encoder and its position inside one mechanical shaft.
After this, the actual position is calculated by keeping track of the position changes.
The actual position can be reproduced uniquely and clearly after the next power-up
only if the encoder position has not moved outside its working area.
Example:
With an absolute multiturn encoder and 12 bits for revolution counting (defined with
parameter
revolutions, or else it will fall below 0 revolutions. If the encoder is run to the position
of -10 revolutions, the position at the next power-up will be 4086 revolutions.
The same situation may occur in a roll-over application with a gear different from a
power of two, because the old and new encoder readings do not give the same
position. This situation can be avoided by activating parameter
TRACKING.
60.05 POS
NUM, 60.07 FEED CONST
(60.03 LOAD GEAR
71.08 GEAR RATIO
(60.02 POS AXIS
POS. If the actual position is out of this range, a fault (POSITION ERROR
SWITCH. If a limit switch is triggered, the speed reference in that
91.03 REV COUNT
UNIT)
DEN)
MUL, 60.04 LOAD GEAR
DIV)
MODE), and
(60.09 POS
60.13 MAXIMUM POS
BITS), the encoder position must not exceed 4096
DIV, 71.07 GEAR RATIO
RESOLUTION).
and
62.05 NEG LIMIT SWITCH
91.06 ABS POS
Drive control and features
59
(60.06
60.14
and