WJLServo said:
99% of applications, regular 2 phase steppers are every bit as good.
But, the 5 phase units do, for reasons I do not understand, run at ~
10X lower velocity ripple when run at equivalent microstep ratio. They
cost too much, they do not have multiple sources, they require non-
standard drive electronics.... but, boy, do they run smooth!
W Letendre
Very probably you can make the motor run by feeding the wires with
five sinusoidal currents, the five phases being equally distributed in
phase. (72 degrees of phase between adjacent phases)
You can identify the phase relationship between the wires by attaching
them to an oscilloscope whilst rotating the shaft of the motor. If
there is no centre-tap terminal to connect to ground during this
experiment then you can connect a resistor (e.g. 1k) from each
terminal to the oscilloscope ground so that mains hum does not
complicate your results.
You could make the sinusoidally controlled current sources either
using linear circuitry (e.g. op-amp and power transistor) or using
switched-mode circuitry. Linear circuitry would probably be easier to
design, but switched-mode circuits would allow less power to be wasted
as heat, and may permit you to obtain better performance from the
motor given a limited amount of power from your power supply.
If there is a centre tap then you could tie that to some voltage to
prevent any of your sinusoidal current sources from saturating,
otherwise you could sense the average terminal voltage by connecting
say 100k resistors in a star configuration from each wire of the motor
to an artificial centre-tap voltage sensing node, and then use an
opamp to slightly adjust the current into one or more of the motor
wires so that the artificial centre-tap that senses the average
voltage of the motor wires remains at a suitable voltage somewhere
roughly in the middle of the supply rails.
To control the five currents into the wires of your motor, and since I
suspect that you want smooth motion, you probably want to use DACs to
generate the sinusoidal signals. You could use five DACs but it is
only necessary to use two DACs, one which generates sine waves (0
degrees phase offset) and another DAC that generates cosine waves (90
degrees phase offset). In order to generate five waveforms with
equally spaced phase offsets, it will be necessari to combine the
outputs from the two DACs in various different proportions, for
example using resistors to sum together different proportions of the
two DAC outputs. In some cases, a negative amount of the DAC output
must be summed, for which purpose an op-amp could be used in an
inverting amplifier configuration. By using two DACs instead of five,
less digital control signals will be required from the computer.
Chris
