This function block is used to both calibrate the index positions of the cyclic position application and to select the Desired Position in the cycle when moving between index positions. The calibration portion of the block arithmetically calculates the Index Length based on the Current Position and the Setup Index. The calculation is performed as follows:

If an ENC Position Point function block is the associated ENC Reference Position selection, the value for the Reference Position is the stored 64-bit Position Point value which, in turn, is referenced to the Cycle Zero position. If an ENC# Cyclic Position function block is the associated ENC Reference Position selection, the Reference Position is also the Cycle Zero.

Using the Index Length, the position selection portion uses the Index value to calculate a Desired Position. The Desired Position value (with the appropriate Reference Position offset ) is then compared to the Current Position generating a Position Error output. The output may then be used for control purposes. A Position Error value of 0.00% indicates you are in the Desired Position.

The Index Length may be set in two ways:

• Manually, by clicking on the Index Length button and setting the 64-bit Index Length using the four 16-bit hexadecimal values Index Length 3, Index Length 2, Index Length 1, Index Length 0.
  
  
• Empirically, by manually moving to one of the index positions. Then, changing the Setup Index to the associated position's Index value. And finally, momentarily activating the Set Index Length which stores the calculated 64-bit Index Length.

After calibration, selecting the Desired Position is achieved by simply setting the Index to the appropriate value. In this example, setting the Index to Position 5. The magenta path above represents the 64-bit count associated with the Desired Position and is calculated as follows:

Resulting in a Position Error calculated as follows:

• Available only in the dw2xx series products
• Requires library: Encoder Control (option -11)
• Requires: Single or Dual Encoder
• Firmware versions 0x2015 and later

This function block may be associated with the following position control function blocks:

• ENC# Cyclic Position
  When selected, the Reference Position offset is zero.
  
  
• ENC Position Point
  When selected, the Reference Position is the 64-bit value stored by the Position Point function block, which in turn, is referenced to the Cycle Zero position.

In either case, the Cycle Length used in the Index Length calculation is obtained either directly from the ENC# Cyclic Position function block or inherited via the ENC Position Point function block.

When this parameter is Set, the 64-bit value calculated by the calibration portion of the function block will be loaded into the Index Length. The Index Length is calculated as follows:

Set this value to the Index associated with the stop position prior to activating the Set Index Length input to calibrate the function block. This value is then used to calculate the Index Length to be used for positioning control.

In most applications, the distance between stop positions is a fixed, constant value. However, it is possible to use varying indices as long as all of the stop positions are defined as some integer multiple of the Index Length.

In this example, we have three different bin sizes which will require moves of different lengths to position properly:

• Each ORANGE bin is one Index Length and located at Index positions 0, 1, 8, 9, 16, 17.
• Each BROWN bin is two Index Lengths and located at Index positions 6 & 14.
• Each GREEN bin is four Index Lengths and located at Index positions 2 & 10.

To calibrate the Index Length for these varying indices applications, the Setup Index must be set properly for the associated position. For the fourth bin position above, the Setup Index must be set to 6 prior to activating the Set Index Length input to calculate the proper Index Length.

Least significant 16-bits of the current 64-bit Index Length which reflects distance between adjacent indices. Concatenate the hexadecimal values to determine the total count.

For example, 0x0000 0x0BA8 0x9DE7 0x3694 = 12,818,831,586,964.

Most, least significant 16-bits of the current 64-bit Index Length which reflects distance between adjacent indices. Concatenate the hexadecimal values to determine the total count.

For example, 0x0000 0x0BA8 0x9DE7 0x3694 = 12,818,831,586,964.

Least, most significant 16-bits of the current 64-bit Index Length which reflects distance between adjacent indices. Concatenate the hexadecimal values to determine the total count.

For example, 0x0000 0x0BA8 0x9DE7 0x3694 = 12,818,831,586,964.

Most significant 16-bits of the current 64-bit Index Length which reflects distance between adjacent indices. Concatenate the hexadecimal values to determine the total count.

For example, 0x0000 0x0BA8 0x9DE7 0x3694 = 12,818,831,586,964.

This parameter sets the multiplier for the Desired Position calculation. If the value exceeds the actual number of positions in the cycle, the resulting move will be the number of complete cycles contained in the Index setting with the final position determined by the remainder.

For example, if the actual number of positions is 18 and the Index is set to 25, the move would be one complete cycle with the final location of Position 7.

The Position Error is generated by comparing the Desired Position to the Current Position as follows:

If the Position Error exceeds +/- 327.66%, the parameter will indicate overrange; however, the 64-bit Internal Count is unaffected.