ADLINK Technology PCI-8154, User Manual

Page: 53 / 228

Operation Theory 43
4.2 Motion Control Modes
Motion control makes the motors run according to a specific speed
profile, path trajectory and synchronous condition with other axes.
The following sections describe the motion control modes of this
motion controller could be performed.
4.2.1 Coordinate system
The Cartesian coordinate is used and pulses are in the unit of
length. The physical length depends on mechanical parts and
motor’s resolution. For example, if a motor is on a screw ball, and
the pitch of screw ball is 10mm and the pulses needed for a round
of motor are 10,000 pulses. One pulse’s physical unit is equal to
10mm/10,000p =1 mm.
Just set a command with 15,000 pulses for motion controller if we
want to move 15mm. How about if we want to move 15.0001mm?
Simple! The motion controller will keep the residue value less
than 1 pulse and add it to next command.
The motion controller sends incremental pulses to motor drivers. It
means that we can only send relative command to motor driver.
But we can solve this problem by calculating the difference
between current position and target position first. Then send the
differences to motor driver. For example, if current position is 1000
and we want to move a motor to 9000, you can use an absolute
command to set a target position of 9000. Inside the motion con-
troller, it will get current position 1000 first then calculate the differ-
ence from target position. The result is +8000. So, the motion
controller will send 8000 pulses to motor driver to move the posi-
tion of 9000.
Sometimes, users need to install a linear scale or external
encoder to check machine’s position. But how do you to build this
coordinate system? If the resolution of external encoder is 10,000