mc1451a-e ETC-unknow, mc1451a-e Datasheet - Page 33

• Manufacturer Part Number: mc1451a-e
• Description: Advanced Brushless Motor Control Chipset
• Manufacturer: ETC-unknow

Commutation Waveforms
The MC1231A supports two commutation waveforms, a 120 degree
offset waveform appropriate for 3-phase brushless motors, and a 90-
degree offset waveform appropriate for 2-phase brushless motors. To
specify the 3-phase brushless waveform the command SET_PHASE_3
is used, and to set it for 2-phase brushless motors the command
SET_PHASE_2 is used.
Depending on the waveform selected, as well as the motor output mode
selected (PWM or DAC16), either 2 or 3 commutated output signals per
axis will be provided by the chipset. The following chart shows this.
Waveform
3-phase
3-phase
2-phase
2-phase
For specific pin assignments of the PWM and DAC16 motor output
signals see the section of this manual entitled 'Pin Descriptions'.
The diagram below shows the phase A, B, and C commutation signals
for a 3-phase brushless motor, and the phase A and phase B signals
for a 2-phase brushless motor.
Commutation Parameters
To perform sinusoidal commutation it is necessary to specify the # of
encoder counts per electrical cycle. To determine this value the # of
magnetic poles on the motor, along with the number of encoder counts
per motor revolution must be known. Knowing these two quantities the
number of encoder counts per electrical cycle is given by the following
equation:
Counts_per_cycle = 2*Counts_per_rot/N_poles
90 Deg
120 Deg
Phase A
Phase A
90
180
Motor Output Mode
PWM
DAC16
PWM
DAC16
Phase B
Phase B
2-Phase Brushless
3-Phase Brushless
270
Phase C
360
# of Output signals
& Name
3 (A, B, C)
2 (A, B)
2 (A, B)
2 (A, B)
33
where:
The command used to set the number of encoder counts per electrical
cycle is SET_PHASE_CNTS. To read back this value use the
command GET_PHASE_CNTS.
The smallest allowed value for the number of counts per electrical
cycle is 129 (decimal).
Index Pulse Referencing
To enhance long term commutation reliability the MC1231A provides
the ability to utilize an index pulse input from the motor encoder as a
reference point during commutation. By using an index pulse during the
phase calculations any long term loss of encoder counts which might
otherwise affect the accuracy of the commutation are automatically
eliminated.
To utilize index pulse referencing the motor encoder chosen must
provide an index pulse signal to the chipset once per rotation. This
index pulse is connected to the chipset using the Index signal of the I/O
chip (see Pin Descriptions section for more information).
Index pulse referencing is recommended for all rotary brushless motors
with quadrature encoders. For linear brushless motors it is generally not
used, although it can be used as long as the index pulses are arranged
so that each pulse occurs at the same phase angle within the
commutation cycle.
When using an index pulse the number of encoder counts per electrical
cycle is not required to be an exact integer. In the case that this value is
not an integer, the nearest integer should be chosen. Conversely, if
index pulses are not being used then the number of counts per
electrical cycle must be an exact integer, with no remainder.
For example if a 6-pole brushless motor is to be used with an encoder
without an index pulse than an encoder with 1200 counts per rotation
would be an appropriate choice, but an encoder with 1024 would not
because 1024 can not be divided by 3 evenly.
Index pulse referencing is performed automatically by the chipset,
regardless of the initialization scheme used (algorithmic, Hall-
based, microstepping, or direct set).
Counts_per_rot is the # of enc. counts per motor rotation
N_poles is the number of motor poles