Product specifications

R01AN0168ED0101 Rev. 01.01 12
Application Note
Chapter 3 About Stepper Motor Movement
The average amplitude of the magnetic field is determined by the PWM duty
cycle, which is represented by the integration of the PWM along its period.
Doing this for both coils, their forces are adding up (red and green
components) to an angle
.
Now, the four
Quadrants are defined in the mathematical way, where quadrant
0 is where both vertical and horizontal currents are positive (angles 0 to
/2),
and quadrant 3 is where vertical current is negative and horizontal current is
positive (angles 3
2 to 2).
3.1.1 Microsteps: Moving the Motor
When moving the motor anchor, a certain amount of Microsteps can be
applied. In hardware, this is related to the resolution of the PWM, which is
applied to the coils. ISM supports a resolution of 4*[2
10
-1] microsteps in PWM
granularity (if directly applied by software), or a subset of 512 or 128
microsteps from those, which can be chosen by the
Channel Management.
Each microstep corresponds to one combination of PWM for the horizontal and
vertical coil, where the vectorized addition of the vertical and horizontal PWM
duty cycles must be a constant, so that the resulting magnetic force is a
constant, too. This is valid for an
ideal motor. For realistic motors, the
combinations of PWM duty cycles may cause variable magnetic forces, in
order to compensate mechanical issues like misalignments etc.
When numbering the microsteps, starting off at angle zero in the positive
mathematical way (“left” turning), the resulting angle of the anchor is
proportional to the microstep number.
Rotation of the motor anchor now is achieved by applying the microsteps in an
incremental sequence. The delay between the microsteps appliance will then
determine the velocity (rotation speed) of the anchor.
An alternative way to rotate the motor is to apply microsteps in constant time
intervals, but to change the velocity (rotation speed), some microsteps are
missed out from the sequence, causing a “jump” of the anchor.
This is the
way how the Channel Management of ISM is performing the motor
rotation.
The direction of rotation is determined by reversing the microstep order.
3.1.2 Macrosteps: Performing several Turns
One Macrostep is defined to be one full turn of the motor’s anchor.
The
Channel Management of ISM defines either 128 or 512 Microsteps for one
Macrostep. This means, that for one turn, it will apply either 128 or 512 PWM
combinations at maximum to the motor coils. It will miss out microsteps, the
faster the turning shall be.
The
Motor Position now is a number of Macrosteps plus Microsteps, because
typically, a stepper motor contains a
gear.
In this way, the motor position is formed to a binary number, with the upper
binary part being the macrosteps, and the lower binary part being the
microsteps.
While the microstep number is determining the PWM combination to be
applied to the motor coils, the macrosteps and microsteps are used for the
motor movement in general (acceleration, velocity etc).