User's Manual

PMAC User Manual
62 Setting Up a Motor
Resolver Feedback
PMAC can accept resolver feedback through its Acc-8D Option 7 resolver-to-digital converter board.
This board, which can be purchased in two-channel and four-channel configurations, processes the
resolver data two ways: first into an absolute word (within one revolution of the resolver), and second,
into a quadrature signal. Both have 4096 counts per electrical cycle of the resolver. An electrical cycle is
a pole-pair, so a 4-pole resolver has two electrical cycles per mechanical revolution, or 8192 counts.
The reading of the absolute word is too slow to perform every servo cycle, so in typical use, this is only
done at power-up/reset, if at all. The ongoing position is received from the quadrature encoder counter to
which the converted quadrature signal has been connected. To the PMAC software, this then looks
exactly like a real quadrature encoder.
For this type of device, PMAC can use the Ix10, I9x, and I8x parameters to read the absolute power-
on/reset position of a single resolver, or of a system of 2 or 3-geared resolvers. If Ix10 is set to 0, the
absolute power-on/reset position read function is disabled, and the power-on/reset position is set to zero,
regardless of the setting of the sensor, and subsequent position readings are incrementally referenced to
this zero position. If the absolute position of a single-turn resolver will be used only to prevent the need
for a power-on phasing search, Ix81 is used to specify the absolute power-on phase position read. For
more information, refer to the Absolute Power-Up Position section in this manual, the Ix10 description in
the Software Reference manual and the Acc-8D Opt 7 R/D Converter manual.
Absolute Power-Up Position
In some applications, it is not permissible or desirable to do a homing search move after power-up or
reset. In these applications, an absolute position sensor can be used so that the true position is known
immediately on power-up/reset and there is no need to move to a known home position. The typical
sensors used for this purpose are absolute encoders and resolvers. PMAC can support absolute power-on
position reading from both of these sensors.
Absolute Position Range
To get absolute power-on position sufficient that no homing search move is required, the position sensor
must be absolute over the entire range of travel of the axis. If the travel covers multiple revolutions of the
motor and the sensor is absolute over only a single turn of the motor, a homing search will still be
required. Although such a sensor can be used for power-on phasing of a brushless motor, for these
purposes, the sensor should be treated as an incremental sensor. See Phasing Referenced to Absolute
Sensor in the Commutation section of this manual, and the descriptions of Ix75 and Ix81 for information
on power-on phasing.
If power-on absolute position of a system is desired without any rollover of the position, the rollover
point(s) of the absolute sensor must be outside the range of travel. If treating the absolute position
information as an unsigned quantity, the rollover points are the zero positions of the sensor. If treating the
absolute position information as a signed quantity, the rollover points are half way in between the zero
positions.
Each Motor x on PMAC has the variables Ix10, I9x, and I8x to support the absolute power-up position
read. Ix10 specifies the register address in PMAC of the absolute sensor, and the method for reading it.
I9x and I8x are used to specify second and third resolvers if a geared resolver system is used to determine
power-on position.