ElmoMC SimplIQ Digital Servo Drives-Bell Command Reference - Manual (Page 222)

Parameter Description
CA[25] Motor
direction:
0: Keep the original motor direction, as connected by the user.
1: Reverse phase driving.
The effect of CA[25] is to set the direction of torque/force for positive
current demand.
With closed loop control, CA[25] and CA[16] (sensor direction) must match so that
positive current will drive the feedback sensor in the positive direction.
4.1.1 Stepper Commutation
With stepper commutation, the transformation angle is set to point at the desired rotor
position. The drive need not be informed where the rotor is; it simply assumes that the
rotor will come to rest at the field position.
Stepper commutation is simple and reliable. Its main drawback is that normally
90
E
o
F
θ θ − << ; therefore, large currents are required to generate a given torque. In its
steady state, the motor torque is zero and not affected by motor current. The sensitivity
of motor torque to deviation of the rotor angle is maximal. The great sensitivity of the
torque to rotor angle generates a fast, but oscillatory position feedback.
4.1.2 Vector Commutation
With vector commutation (for 3-phase or 2-phase motors), the windings field is set to
point 90º away from the rotor position and the drive must know where the rotor is in
order to maintain this field direction.
The advantage of vector commutation is its maximum torque per given motor current,
and its smooth, controllable torque. It is ideal for servo applications. Vector calculations
involve a considerable amount of real-time calculation and requires a rotor position
sensor. The torque is not sensitive to rotor angle.
Most brushless motors have two or three phases (coils, or windings).
The SimplIQ drive supports both types.
For three-phase motors, the phases are called A, B and C.
For two-phase motors, the phases are called A and B .
When the rotor travels, the transformation angle rotates. The coils of the three-phase
motor are powered in the sequence A-B-C-A-B-C . . . (or A-B-A-B... for two phase motors)
and so on.
You can read the electrical and mechanical angle of the motor using the following
commands:
SimplIQ for Steppers Application Note Commutation and Pole Identification
MAN-STECR (Ver. 1.1)
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