ADLINK PCI-8158 - Manual (Page 55)

Operation Theory 45
4.2 Motion Control Modes
Motor control is not only for positive or negative moving, motion
control can make 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 system and pulses for the unit of length
are used . The physical length depends on mechanical parts and
motor’s resolution. For example, if the motor is installed on a
screw ball. The pitch of screw ball is 10mm and the pulses needed
for a round of motor are 10,000 pulses. We can say the physical
unit of one pulse is equal to 10mm/10,000p =1 micro-meter.
Simply set a command with 15,000 pulses for motion controller to
move 15mm. How about if we want to move 15.0001mm? The
motion controller will keep the residual 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. We want to move a motor to 9000. User can use an abso-
lute command to set a target position of 9000. Inside the motion
controller, it will get current position 1000 first then calculate the
difference from target position. It gets a result of +8000. So, the
motion controller will send 8000 pulses to motor driver to move the
position of 9000.
Sometimes, you may 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