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OTION
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SMD23E2 and SMD24E2 User’s Manual
ADVANCED MICRO CONTROLS INC.
40
Synchrostep (Virtual Axis) Moves
On controllers that support motion axis programming, such as the Rockwell Automation ControlLogix plat-
forms, an SMD23E2 or SMD24E2 can be tied to the motion axis, with the host controller periodically send-
ing position and velocity data to the unit as part of the axis update. The loop is closed by the SMD23E2 or
SMD24E2 by controlling the velocity of the motor. Both linear and circular axes are supported.
Linear and Circular Synchrostep Moves have the following parameters and characteristics:
Position and Velocity are programmed as 32 bit double integer values.
The loop can be closed with respect to the internal motor position.
The loop can be closed with respect to the encoder position on units that have the encoder option.
A proportional constant is available to control the sharpness of the control.
AMCI suggests a value of 1 or 2 when using the motor position to control the loop.
AMCI suggests a value between 10 and 50 when using the encoder position to control the loop.
A network delay value that can be used to offset some of the network delays incurred when communi-
cating with the SMD23E2 or SMD24E2. Programmed in milliseconds, using this value is optional and
defaults to zero. If used, a good starting point is the update time of the connection in milliseconds. The
range of this parameter is 0 to 20.
Circular Synchrostep Moves have one additional parameter. This parameter is often called the “Position
Unwind” value, and it defines the point at which the position rolls over and returns to zero. On the SMD23E2
or SMD24E2 units, this parameter has a range of 21 to 65,535.
When using the SMD23E2 or SMD24E2 as an axis follower, it is best to run the virtual axis as
a high priority event driven periodic task.
When using the SMD23E2 or SMD24E2 as an axis follower, it is best to configure the unit to
have a starting speed of 1. This will reduce jitter in the motor position at slow speeds or when
the position is near its target.
When using the SMD23E2 or SMD24E2 as an axis follower, the programmed acceleration
and deceleration values determine the response time of the internal closed loop algorithm.
A suggested starting value for the Acceleration and Deceleration Parameters is Motor
Resolution / 10.
When using the SMD23E2 or SMD24E2 as a linear axis follower, use caution in systems that
always rotate in the same direction. If the position value overflows, it will switch from the
maximum positive value to the maximum negative value and unpredictable motion may occur.
https://www.amci.com/industrial-automation-support/sample-programs/
. It can be
found in the
Stepper Motor Control
section of that page. The sample includes the setup required to run the
axis as a high priority event driven periodic task. If you are using a different host controller that supports
motion axis programming, feel free to contact AMCI technical support for assistance in programming your
controller.
Blended Moves offer you similar functionality to linear motion axes when the move profile is well defined
before the move begins. Consider using this functionality for simple linear profiles. A Blend Move is pro-
grammed into an SMD23E2 or SMD24E2 before it is run and the unit precisely controls position and velocity
throughout the entire move. Additional information on
functionality can be found starting on
