Control Techniques Nidec SI-EtherCAT User Manual page 126

8.6.5 Window Filter
A window filter before interpolation can be enabled when the application requires. If the window
filter is enabled, the target values are fed through a window filter, the output of that window filter is
then the input to the interpolation.
Table 8-10 Window Filter Size
0x300A Window Filter Size
Access: RW
Default: 0
PDO Mappable: No
2. = Disable window filter
3. = Window filter size 2 x interpolation period
Description: 4. = Window Filter size 4 x interpolation period
5. = Window Filter size 8 x interpolation period
6. = Window Filter size 16 x interpolation period
The Window filter follows the following equations:
X(n)
Y (n) = Y ( n - 1) +
s
X(n)
Y (n) = Y ( n - 1) +
s
Y (0) + X (0) when n = 0
Where:
• n is the iteration i.e. increments after each new target position arrives. n = 0 when
entering CiA402 operational state.
• Y(n) is the window filter output at the nth iteration of the filter.
• Y(n-1) is the window filter output at the (n-1)th iteration (i.e. the previous iteration)
• X(n) is the window filter input at the nth iteration of the filter.
• S is a constant, the size of the filter
• X(n-S) is the window filter input at the (n-S) iteration.
The window filter is executed at the rate of the EtherCAT cycle time; hence it operates before the
interpolator.
One of the side effects of the window filter is to add a delay in the feedback loop.
NOTE
Therefore, the following error, as seen by the PLC, will be increase by the length of the
filter. The EtherCAT module does not hide this fact so it will impact on status word target
reached flag which will no longer indicate target reached if the increase in following
error exceeds the position window object setting (0x6067).
126
Range: 0 to 4
X(n-S)
- When n>S
s
X(0)
- When n<=S
s
Size: 1 byte
Type: Unsigned integer / USINT
Update Rate: New value used on CiA402 transition
to SWITCH_ON
SI-EtherCAT User Guide
Unit: N/A