Homing 使用初始值

Using the Origin Variable

In servo control applications, the Command and Actual Positions for an Axis are generally used for position error calculations. On each sample, the controller reads the new Actual Positions from the feedback devices and calculates the new Command Positions.

To determine the relationship between Command and Actual Positions for an Axis and physical positions on the machine, you can use the Origin variable (which can be set by the host).为了确定命令和实际位置的关系，可以使用origin 变量。

If it is important to set the Command or Actual Position to an exact value, you should use thempiAxisOriginSet(...) function. Calling mpiAxisOriginSet(...) will modify both Command and Actual Positions by the same amount.

The Origin variable can be set in two different ways depending on the desired result. For example, assume the Command and Actual Positions are 10,000 and 10,024 counts respectively and that the axis is not moving. 

Setting the Origin variable to 10,000 will result in Command Position = 0 and Actual Position = 24. Setting the Origin variable to 10,024 will result in Command Position = -24 and Actual Position = 0. 

This second method is the most frequently used method for setting the new Origin after homing. Refer to the next table.

Position and Velocity criteria for generating motion completion events

If Command Position =

If Actual PositionAnd you set Origin VariableThen Command Position =

And Actual Position =

10,000

10,024

10,000

0

24

10,000

10,024

10,024

-24

0

Cautions about motion in general:

 

1. During motion, you should never call the mpiAxis[Actual|Command]PositionSet(...) ormpiAxisCommandOriginSet(...) functions. 
   
   
2. Setting a new Position using mpiAxisCommandPositionSet(...) ormpiAxisActualPositionSet(...) should be done with caution, because the controller will immediately try to servo to the new position. If the new and old command positions differ by a large amount the axis may fault (limit error) or jump to the new position at very high speed. Setting new positions with mpiAxisOriginSet(...) or mpiAxisCommandOriginSet(...) will not cause a jump.
   使用mpiAxisOriginSet(...) or mpiAxisCommandOriginSet(...) 不会导致电机跳跃
3. The effect of any origin or position set functions calls will not be seen by the host until the next controller sample following the call. 
   
   
4. Calling mpiAxisOriginSet() while an axis is in motion will change the final target position's value. This will not change the trajectory however. If the axis was to originally move 5000 counts, then the axis will still move a total of five thousand counts. 在运动过程中调用mpiAxisOriginSet()，不会导致最终目标位置的改变。
   
   Start 
   Position
   Actual 
   Position
   End 
   Position
   Comment
   0
   0
   5000
   The beginning of a 5000 count move, origin currently 0.
   0
   2500
   5000
   Origin is about to be set to 2000.
   -2000
   500
   3000
   Origin has been changed to 2000.终止位置相应改变
   -2000
   3000
   3000
   Motion is complete. Distance traveled still 5000 counts.