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Operation Theory 45
4.2 Motion Control Modes
Not like motor control is only for positive or negative moving,
motion control 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
We use Cartesian coordinate and pulses for the unit of length. The
physical length depends on mechanical parts and motor’s resolu-
tion. For example, if users install a motor 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 that one pulse’s physical
unit is equal to 10mm/10,000p =1 micro-meter.
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?
Don’t worry about that, 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. 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, users need to install a linear scale or external
encoder to check machine’s position. But how do you to build this