
12
SM-Universal Encoder Plus User Guide
www.controltechniques.com
Issue Number: 6
3.4.3
SinCos Signal Values
When operating with a SinCos encoder, which has no comms or commutation signal
inputs (Pr
x.15
= 6), the internal differential SinCos signal values are written to both
Pr
x.42
(Sin) and Pr
x.43
(Cos) as an unsigned numbers.
For further details refer to both Pr
x.42
and Pr
x.43
3.4.4
Incremental plus commutation, (absolute encoders) Ab.SErvo, Fd.SErvo,
Fr.SErvo and SC.SErvo.
The incremental encoder with commutation works in the same way as the incremental
encoder except that multiple channels are used to give a discrete code for every
position increment.
When operating the drive in closed loop servo absolute position of the machine shaft is
required as soon as the drive is enabled. Because the marker signal is not effective until
the shaft passes a particular position, this cannot be used to determine the absolute
position. Therefore an encoder with additional commutation is required.
Therefore with a 6 pole machine the U, V and W commutation signals will repeat three
times per mechanical revolution, or with an 8 pole machine four times per mechanical
revolution etc.
The U, V and W commutation signals are used when the drive is enabled to locate the
position of the machine shaft within 60
°
electrical so that the current vector can be
applied within 30
°
electrical either side of the correct position for maximum torque
production. At certain positions of the shaft, the torque capability of the drive during this
period is reduced to 0.866 of the nominal level during initialisation.
Once the shaft has moved through a maximum of 60
°
electrical, one of the U, V or W
signals will change state. The location of the waveform edge is used to locate the
machine position exactly. This information is then stored by the option module and used
until power-down to place the current vector in the correct position for maximum torque.
To ensure that this process is carried out correctly the control algorithm waits for two
changes of the state of the U,V and W waveforms, at this point there will be no
additional torque ripple and maximum torque is available for all shaft positions.
Using this type of encoder does not result in any jump in position when the drive is first
enabled after power-up, but only the small reduction in specification described above for
the first 60 to 120
°
electrical of movement.
Type
Encoder
Description
Pr x.15
Incremental
plus
commutation
(absolute
encoders)
Ab.SErvo
Quadrature incremental encoder with commutation
outputs.
With or without marker pulse.
3
Fd.SErvo
Incremental encoder with frequency, direction and
commutation outputs.
With or without marker pulse.
4
Fr.SErvo
Incremental encoder with forward, reverse and
commutation outputs
With or without marker pulse.
5
SC.SErvo
Absolute SinCos encoder plus commutation signals
without marker pulse.
12
The U, V and W commutation signals should have a period that is one electrical
revolution as shown in Figure 3-6.
NOTE
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