Logosol Absolute Positioning Servo Drive LS-173AP
Doc # 712173008 / Rev. 1.06, 05/09/2002
Logosol, Inc.
••
1155 Tasman Drive
••
Sunnyvale, CA 94089 Tel: (408) 744-0974
••
www.logosolinc.com 17
Group Addresses
In addition to the individual address, each controller has a secondary group address. Several
LS-173AP controllers may share a common group address. This address is useful for sending
commands, which must be performed simultaneously by a number of drivers (e.g.
Start
motion, Set Baud Rate
, etc.). When a LS-173AP
receives a command sent to its group
address, it will execute the command but not send back a status packet. This prevents data
collisions on the shared response line. When programming group addresses, however, the
host can specify that one member of the group is the “group leader”. The group leader will
send back a status packet just like it would for a command sent to its individual address. The
group address is programmed at the same time as the unique individual address using the
Set
Address
command.
Multiple Controller Configuration
Communication Rate
The default baud rate after power-up is 19.2 Kbps. Baud rates up to 115.2 Kbps may be used
at maximum servo rate. After communication has been established with all servo drives on a
single network, the baud rate may be changed to a higher value with the
Set Baud Rate
command.
Servo Control
LS-173AP uses a “proportional-integral-derivative”, or PID filter. The PWM signal is a square
wave with 51.2 µsec period and varying duty cycle. The PWM value is between 0 and 1023 (0
to 100% duty cycle). Usually, to have better motor control, duty cycle more than 90% is not
recommended. The position, velocity and acceleration are programmed as 32-bit quantities in
units of encoder counts for servo ticks. For example, a velocity of one revolution per second of
a motor with a 500 line encoder (2000 counts/rev) at a tick time of 0.512 msec. would
correspond to a velocity of 1.0240 counts/tick. Velocities and accelerations use the lower 16
bits as a fractional component so the actual programmed velocity would be 1.024 x 2
16
or
67,109. An acceleration of 4 rev/sec/sec (which would bring us up to the desired speed in ¼
sec) would be 0.0021 counts/tick/tick; with the lower 16 bits the fractional component, this
