Beta 1742A Manual do Utilizador descarregar pdf (Página 508)

100

101

G-2 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual

–

January 2001 GFK-1742A

A = Acceleration/deceleration during the strobe event which is 250,000,000

cnts/sec

(assumed to be constant over the entire 250

s period; Larger

acceleration values will increase the amount of error in the calculation)

= Position sampling period which is 250 microseconds

= Initial velocity just before the strobe event which will be 0 for this example.

The change in the number of encoder counts (Cnts) for a given amount of time (t) can be

calculated using the following formula:

act

= V

t + ½ A t

Therefore the total number of counts to occur during the sampling period for this example

is approximately 8 counts (actual calculated values is 7.8125) or 0.343 degrees of motor

rotation.

The average velocity for the sample period given the change in position would be as

follows:

avg

= Change in counts = 7.8125 cnts = 31250 cnts/sec

Sampling Period 250

sec

The following formula can be used to estimate the strobe position using the velocity

derived above:

est

= V

t + V

avg

Therefore, the error between the estimated strobe position and the actual strobe position is

as follows:

Error = P

act

- P

est

The graph below contains plots of the actual position, the estimated position, and the

resulting strobe position count error for the 250 microsecond sample period. From the

graph, it is evident that the greatest count error occurs in the middle (i.e. at 125

microseconds) of the time period.

1 2 ... 503 504 505 506 507 508 509 510 511 512 513 ... 519 520

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