MOTION CONTROL
SMD17E2 User 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 SMD17E2 can be tied to the motion axis, with the host controller periodically sending position and
velocity data to the unit as part of the axis update. The loop is closed by the SMD17E2 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 SMD17E2. 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 SMD17E2
units, this parameter has a range of 21 to 65,535.
When using the SMD17E2 as an axis follower, it is best to run the virtual axis as a high prior-
ity event driven periodic task.
When using the SMD17E2 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 SMD17E2 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 SMD17E2 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 posi-
tive value to the maximum negative value and unpredictable motion may occur.
A sample program that demonstrates virtual axis programming on the ControlLogix platform is available on
the AMCI website at 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 the SMD17E2 before it is run and the unit precisely controls position and velocity throughout
the entire move. Additional information on
Blend Move functionality can be found starting on page 35.
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