Actuator commands

Estimating precision for controlling actuators

The global communication delay of an output in relation to the crossing of a mechanical threshold depends on the application. It may be divided into two parts:

Minimum delay: is a constant part corresponding to the time necessary to set the outputs.
Max/min delay: a variable part corresponding to the "jitter" brought by the periodicity of the refreshing of outputs. Internal module synchronization is such that the variable part is reduced to the influence of T0 (period between two encoder pulses) and of T2 (calculation period).

Minimum delay (1)

in incremental encoder	= T2+T3
in absolute encoder	= T1 + T2 + T3

Maximum / minimum delta (2)

without anticipation	= T0 + T2
with anticipation of the SSI	= 2 x (T0 = T2)
with anticipation of the incremental	= 2 x T0 = T2

Precision in output control

The switching delay on outputs causes an error in relation to the target threshold.

Illustration of the use of the without anticipation function

The switching zone deviates from the target threshold proportionally to the speed.

Switching can be reset around the threshold using the anticipation system. To do this, simply add to the anticipation value = minimum delay (1 + 1/2 delta delay (2).

1	Minimum delay
2	Maximum / Minimum delay
3	Fixed deviation
4	Delta switching

Illustration of the use of the with anticipation function

NOTE: To make a valid correction to the delay caused by the module, the encoder resolution should be 2 to 5 times more precise than that which was estimated at the first attempt.

Calculation chart

The tables below show the foreseeable errors depending on the application type and for a reference speed of 120m/min. Values for other speeds can be obtained by a simple rule of three.

Fixed deviation for a speed of 120 m/mn (encoder resolution = 0.1 mm)

Calculation	No. of cams	incremental	SSI 50 (1)	SSI 100 (1)	SSI 200 (1)
50 (1)	up to 16	0.4 mm	0.5 mm	-	-
100 (1)	up to 32	0.5 mm	0.6 mm	0.7 mm	-
200 (1)	up to 128	0.7 mm	0.8 mm	0.9 mm	1.1 mm

Delta switching for a speed of 120 m/min without anticipation (encoder resolution = 0.1 mm)

Calculation	No. of cams	incremental	SSI 50 (1)	SSI 100 (1)	SSI 200 (1)
50 (1)	up to 16	0.2 mm	0.2 mm	-	-
100 (1)	up to 32	0.3 mm	0.3 mm	0.3 mm	-
200 (1)	up to 128	0.5 mm	0.5 mm	0.5 mm	0.5 mm

1 Values are expressed in micro seconds.

WARNING

UNEXPECTED APPLICATION BEHAVIOR - DELTA SWITCHING VARIATION

The variation in communication (Delta switching) is increased if the anticipation system is used.

Failure to follow these instructions can result in death, serious injury, or equipment damage.