Motion Control Instructions General Rules For Motion Control Function Blocks - Allen-Bradley Micro800 General Instructions Manual

Chapter 17
Motion control instructions
General rules for motion
control function blocks
Rule applies to
Input parameters
Missing input parameters
Inputs exceeding application limits
Sign rules for inputs
Position versus Distance
Position/Distance input
Velocity input
Direction input
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The general rules for the Micro800 motion control function blocks follow the
PLCopen Motion control specifications. The following table provides general
rules about the interface of motion control function blocks.
Rule
With Execute: The parameters are used with the rising edge of the execute input. To modify any parameter, change the input
parameter(s) and trigger the motion again.
Note: If an instance of a function block receives a new Execute before it finishes (as a series of commands on the same instance),
the new Execute is ignored, and the previously issued instruction continues with its execution.
With Enable: The parameters are used with the rising edge of the enable input and can be modified continuously.
Missing input is captured during User Application compilation. There is no missing input error handling at the controller level.
If a function block is commanded with parameters that result in a violation of application limits, the instance of the function
block generates an error. In this case, the Error output is flagged On, and error information is indicated by the output ErrorID. The
controller, in most cases, remains in Run mode, and there is no Motion Error reported as a major controller fault.
The Acceleration, Deceleration, and Jerk inputs are always positive values. Velocity, Position and Distance inputs can have
positive and negative values.
Position is a value defined within a coordinate system. Distance is a relative measure related to technical units. Distance is the
difference between two positions.
Only linear motion is supported on Micro800 controllers. For MC_MoveAbsolute function block, the position input is the absolute
location to be commanded to the axis. For MC_MoveRelative, the distance input is the relative location (considering current axis
position is 0) from current position.
Velocity can be a signed value, but it can also use Direction input to define the sign of the velocity (negative velocity x negative
direction = positive velocity). The E parameter "Direction" refers to the velocity input and output for compatibility reasons.
For distance (position) motion, with the target position (either absolute, or relative) defined, the motion direction is unique. The
direction input for distance move is ignored.
For velocity motion, direction input value can be 1 (positive direction), 0 (current direction) or -1 (negative direction). For any
other value, only the sign is considered. For example, -3 denotes negative direction, +2 denotes positive direction, and so on.
For velocity move (MC_MoveVelocity), the sign (velocity x direction) determines the actual motion direction if the value is not 0.
For example, if velocity x direction = +300, then direction is positive.
Rockwell Automation Publication 2080-RM001D-EN-E - February 2015