– 5 –
Full Coil
versus
Half Coil, cont.
Danaher Motion
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Precision Systems Group
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7C Raymond Avenue, Salem, NH 03079
tel:
603.893.0588
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toll free:
800.227.1066
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fax:
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url:
www.danaherprecision.com
The circuit path for the Direction line is screened on the
module exterior; it begins at the user su5 volts (pin
#10), flows through the internal opto-isolator LED and resistor,
and is brought out at the Direction pin (#8). Accordingly, the
default (unterminated) state of this input is a logic high (+5
volts). The Direction input must accordingly be driven by a
device capable of sinking current; 16 milliamps is required
to turn on the opto LED. A typical I.C. which meets these
requirements is a TTL 7406 or 74LS06; most other TTL chips
are also capable of sinking 16 milliamps. Note that the
Direction (and Step Pulse) lines are opto-isolated; whenever
possible, the ground for the device driving the Direction line
should be isolated with respect to Power Supply Ground. In
this manner, the controlling circuitry (often a noise sensitive
CPU based system) will be totally isolated from the motor
drive circuits.
Pin #9 Step Pulse
The stepping motor will rotate one step (full, half or microstep,
depending on model and mode of operation) for each falling
edge (high to low transition) received on the Step Pulse input.
The direction of rotation will depend on the level on the
Direction line, as previously discussed. The electrical charac-
teristics of the Step Pulse input are identical to those of the
Direction input (see above), with the one exception that transi-
tions must be rapid in nature; the high to low transition should
occur in 200 nanoseconds or less. Slow transition devices such
as most opto-isolators, op-amps, etc. are too slow and should
not be used. The minimum duration of the Step Pulse line in
either the low or high state 1 is microsecond. This results in a
maximum input frequency of 500 kHz. Many pulse generators
will be incapable of producing such high frequency pulse
trains (our PCX card for the IBM-PC is an exception, with a 524
kHz maximum step rate). 300 kHz corresponds to a shaft rota-
tion rate (using the divide by 10 HDM7) of 150 revolutions per
second, or 9000 rpm. While little usable shaft power remains at
such speeds, the ability of our MDM7 to run stepping motors at
such speeds (a 50 volt power supply and a modest accelera-
tion helps) demonstrates the inherently high performance of
these drives. The SDM7 will perform similarly with a 30 KHz
input step rate. Note: Do not bundle the Step and Direction sig-
nals within the same cable as the motor leads; this may result
in signal noise and erratic operation. Use separate cables, and
employ a shield around the motor leads; this shield should be
tied to Power Supply Ground and the module case.
Pin #10 .5 Volts D.C.
The user must p5 volts D.C. to this pin to operate the
opto-isolators. The circuit path shown on the module exterior is
all that this +5 volt supply operates; the aurrent requirement is
accordingly ~35 milliamps. As previously noted, this +5 volt supply
should be floating (isolated) with respect to Power Supply
Ground to fully utilize the isolation provided by the opto coupled
inputs.
Pin #11 Current Set
The motor current is determined by the value of a 1/4 watt
resistor which is installed between pins #11 (Current Set) and
#12 (Power Supply Ground). The value chosen for this resistor
is a function of the motors rated (nameplate) phase current and
the coil drive mode (full coil or half coil).
The relationship between motor rated current, drive mode, and
resistor value is as follows:
Current Set Resistor Table
Pull Coil
Half Coil
Resistor
1.5A
.75A
12K
2.0A
1.00A
15K
2.5A
1.25A
27K
3.0A
1.50A
33K
3.5A
1.75A
47K
4.0A
2.00A
68K
4.5A
2.25A
82K
5.0A
2.50A
120K
5.5A
2.75A
180K
6.0A
3.00A
270K
6.5A
3.25A
560K
7.0A
3.S0A
3.3M
The above chart is also screened onto the exterior of the drive
module. As an example, a popular 100 oz-in motor is rated at 1.8
Amps per phase. Operation in half coil mode will require a 47K
ohm resistor, while full coil operation will require a 12K or 15K
ohm resistor. The highest motor phase current operable with
these modules will be 7.0 Amps per phase, although motors of
this current rating could only be run in full coil mode. To pre-
serve the highest possible microstep uniformity when using the
MDM-7 drive, do not vary the resistor value from that indicated
in the table. If you happen to be using a 4 lead motor, the rated
(nameplate) current rating will correspond to the half-coil col-
umn resistor value. Note that while the resistor sets the motor
operating current (and hence torque) at standstill and through-
out the low speed region (see above), high speed torque is
inductively limited and hence independant of the specific resis-
tor setting.
In some applications, it may be desirable to lower the motor
current when stationary, restoring it to its full value only when a
move is required. This can be achieved by paralleling a second
resistor with the current set resistor. Total torque shut-off can
be achieved by applying a short (zero resistance) across the
current set resistor. Since the Current Set pin is referenced to
Power Supply Ground, an opto isolator will be necessary if full
isolation is to be preserved. A typical implementation is shown
in Figure 03:
In applications where full acceleration torque is required,
enabling full current 10-20 milliseconds before initiating a move
