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G320 REV-7

Click here to download this manual
(PDF)

G320 Revision 7
Manual
Last Update: July 15, 2010

Thank you for
purchasing the G320 drive. The G320 DC servo drive is warranted to be free of
manufacturing defects for 1 year from the date of purchase. Any customer who is
dissatisfied with it or is unable to make it work will be cheerfully refunded
the purchase price if the G320 is returned within 15 days of the purchase
date.

PLEASE READ FIRST BEFORE USING THE G320:

If
you are not familiar with DC servo drives please do the following setup
instructions with the motor on the bench before mounting it on the mechanism it
will eventually run. This will allow you to get a baseline motor behavior of
what to expect.

Before you start, you must have a suitable encoder
mounted and properly aligned on the motor. Follow the manufacturer’s
instructions on mounting and aligning the encoder if the motor doesn’t already
come with one.

Next you must have a DC power supply suitable for the
motor. The power supply current rating must equal the maximum current you expect
to run the motor at.

Finally, have a STEP and DIRECTION pulse source
available.

Before going on, turn the current LIMIT trimpot a quarter to
half of full scale. Turn the GAIN trimpot fully off and turn the DAMP trimpot to
a quarter of full scale. The trimpots are single-turn so be careful not to
over-torque them.

G320 PINOUT

TERMINAL 1
Power Ground
Connect the negative (black) lead of your power supply
to this terminal.

TERMINAL 2 Power (+)
Connect the
positive (red) lead of your power supply to this terminal. It must be between
+18VDC to +80VDC.

TERMINAL 3 Armature (-)
Connect the
black lead of your motor to this terminal.

TERMINAL 4
Armature (+)
Connect the red lead of your motor to this
terminal.

TERMINAL 5 ERR/RES
This is the ERROR and
RESET pin. For a full explanation read the section titled “ERROR/RESET PIN” on
page 5.

TERMINAL 6 Encoder Ground
Connect the encoder
power supply ground to this terminal.

TERMINAL 7 Encoder
+5VDC
Connect the encoder +5VDC pin to this terminal.

TERMINAL
8 Channel A
Connect the Channel A pin of your encoder to this
terminal.

TERMINAL 9 Channel B
Connect the Channel B
pin of your encoder to this terminal.

TERMINAL 10
Direction
Connect the DIRECTION signal to this
terminal.

TERMINAL 11 Step
Connect the STEP signal to
this terminal.

TERMINAL 12 S/D Common
Connect this
terminal to +5VDC.

IMPORTANT: When first testing the G320,
connect ERR/RES (term. 5) to ENC+ (term. 7). Please follow the next steps in the
sequence they are given.

STEP 1: CONNECTING THE
ENCODER

The encoder must be a digital quadrature TTL output type
that operates on a single +5VDC power supply and the power supply current rating
must be less than 50 mA if it is being powered by the G320. It should be at
least a 200 line encoder. If the encoder supply current is more than 50 mA, use
an external +5VDC supply. IMPORTANT: Connect a 470 ohm resistor from TERMINAL 6
to TERMINAL 7 if an external power supply is used for the
encoder.

TERMINAL 6 ENC-
Connect the encoder power
supply ground to this terminal.

TERMINAL 7 ENC+

Connect the encoder +5VDC to this terminal

TERMINAL
8 Phase A
Connect the encoder phase “A” to this
terminal

TERMINAL 9 Phase B
Connect the encoder
phase “B” to this terminal

To determine the optimal encoder line count,
please follow the instructions below.

1.) Determine motors no load
RPM
2.) Calculate rated RPM as 80% of no load RPM
3.) Divide (#2) by 60 to
get revolutions per second
4.) Determine the CNC program’s maximum step pulse
frequency (in Hz)
5.) Divide (#4) by (#3), which will give you the maximum
counts per revolution
6.) Divide (#5) by 4, which will give you the max line
count
7.) Pick the first standard line count below (#6)

An example of
using that formula with a 45kHz step pulse frequency and a maximum motor RPM of
3000:

(45kHz / 40) / 4 = 281.25

STEP 2: CONNECTING THE
POWER SUPPLY

CAUTION! Never put a switch on the DC side
of the power supply! This will damage, if not destroy, your
drive!

Keep the power supply leads short and use the largest
wire gauge that will fit in the terminals. If the lead length is more than 18”
use a 1000 uF capacitor across the G320 power supply terminals. Make sure your
power supply can provide the peak current the motor may draw. The power supply
voltage must be between 18 VDC and 80 VDC. The actual voltage should not be more
than 5 volts higher than the motor’s rated voltage.

TERMINAL 1
Power Ground
Connect the negative (black) lead of your power supply
to this terminal.

TERMINAL 2 Power (+)
Connect the
positive (red) lead of your power supply to this terminal. It must be between
+18VDC to +80VDC.

STEP 3: TESTING THE ENCODER

At
this point the encoder should be tested for functionality. If you wish to
monitor the POSITION ERROR test point with a voltmeter or oscilloscope, then
remove the cover of the drive now. If you have a choice, pick the
oscilloscope.

The POSITION ERROR test point shows the difference between
the command position and the actual motor position. When both are the same, the
voltage will be +5VDC. For every count the motor is clockwise of the command
position, the voltage will decrease by 0.04 volts. When it drops to 0.4 volts,
the protection circuit takes over and resets the drive for 3 seconds. While in
reset mode, the FAULT light is on.

For counter-clockwise position errors
the voltage will increase by 0.04 volts for every count until it reaches 9.6
volts when again the protection circuit takes over as before.

VOLTMETER
MONITORING: Place the red lead on the test point and the black lead on the large
blue capacitor lead (GND) furthest from the main connector. Turn on the power
supply. The FAULT light should be on for 3 seconds and then turn off. The
voltmeter should read +5VDC. Turn the motor shaft clockwise VERY slowly. The
voltmeter reading should decrease 0.04 volts for every encoder count. When the
reading reaches 0.4 volts, the red light will turn on and the voltage will jump
back to +5VDC. After 3 seconds the light will turn off. You may turn the motor
shaft counter-clockwise as well. The voltage will increase then by 0.04 volts
per count until it reaches 9.6 volts and trips the protection
circuit.

OSCILLOSCPE MONITORING: Set the scope to 2 volts / cm vertical
and about 1 millisecond per cm horizontal. Zero the trace to the bottom line on
the screen. DC couple the input. Place the probe on the test point and the
ground clip to the blue capacitor ground lead. Follow the steps in VOLTMETER
TESTING above.

STEP 4: CONNECTING CONTROL
INPUTS

The control input group is the standard step motor drive
STEP, DIRECTION and +5VDC lines. The STEP and DIRECTION signal drivers must be
TTL compatible and have edge transition times of 100 ns or faster. The +5VDC is
the opto-isolator common anode line and must be returned to the pulse source
+5VDC supply.

TERMINAL 10 Direction
Connect the
DIRECTION line to this terminal.

TERMINAL 11 Step

Connect the STEP line to this terminal.

TERMINAL 12
Common
Connect this terminal to the controller +5VDC power
supply

STEP 5: TESTING THE CONTROL INPUTS

You may
wish to test the functionality of these inputs. If you used an oscilloscope in
the previous section, leave it connected to the test point. If you used a
voltmeter, then remove it from the drive.

Set the STEP pulse generator to
about 40 pulses per second and set the DIRECTION output to clockwise (logical
“1”). Turn on the power supply. After the power-on reset period of 5 seconds the
FAULT light will turn off.

If you are using an oscilloscope, then the
test point voltage will begin to increase until 3 seconds later it trips the
protection circuit at 9.6 volts. The FAULT light will turn on for 5 seconds and
voltage will snap back to +5VDC. After the FAULT turns off, the sequence will
repeat again.

If you are not using an oscilloscope, just see if the FAULT
light turns on and off every three seconds.

STEP 6: CONNECTING
THE MOTOR

Make sure the power is off and the STEP pulse source
is set to zero pulses per second. Check to see if the trimpot settings are set
according to the instructions on page 2. You may wish to secure the motor so it
can’t jump off the bench.

TERMINAL 3 Armature
(-)
Connect the BLACK motor lead to this terminal.

TERMINAL
4 Armature (+)
Connect the RED motor lead to this
terminal.

STEP 7: TUNING THE SERVO

Turn on the
power supply. The FAULT light should turn off after 3 seconds. If everything is
correct there should be an audible “singing” noise coming from your motor. This
is normal. The motor is dithering or bouncing between adjacent encoder counts.
The integral term in a PID loop has infinite DC gain over time and will amplify
even the smallest position error. Because encoder feedback can only occur on
count edges, the loop is “blind” until it encounters an encoder count edge. It
then reverses the motor direction until another edge is found, then the process
repeats.

If the motor jumps slightly and the FAULT light immediately
turns back on, then either the motor is wired backwards or the trimpots are
misadjusted. Check the trimpot settings. If they seem right then switch the
motor leads and try again. If it still doesn’t work and all the previous steps
have been followed, call Geckodrive Support at the number at the end of this
document.

Now turn on your STEP pulse source and ramp the speed up to see
if the motor turns. It should turn clockwise with a logical “1” on the DIRECTION
input.

The optimum way to tune the servo is to induce an impulse load on
the motor while watching an oscilloscope to see how the motor behaves in
response, then adjusting the PID co-efficient for optimal behavior.

In all cases the motor must return to the command
position, what matters is how it does it. The manner in which the motor returns
to its command position is called damping. At one extreme, called over damped
response, the motor returns to position after a long, drawn out delay. At the
other extreme, called under damped response, the motor returns to its position
too rapidly, overshoots, returns and undershoots and so on until it finally
settles at its command position. This is also called ringing; when extreme, the
over/undershoot builds in amplitude until the motor enters violent oscillation.
Between the two extremes is the optimal response called critical damping. Here
the motor rapidly returns to its position with little or no overshoot in the
minimal amount of time.

POSITION ERROR TEST POINT NOTE:

Don’t
confuse the POSITION ERROR with the motor or machine position. The signal is
actually the differential position error between the command speed and the motor
speed. As noted above, sending clockwise STEP pulses moves the POSITION ERROR
voltage more positive while turning the motor clockwise moves the POSITION ERROR
voltage more negative.

When the motor encoder counts match the number of
STEP pulses being sent one for one, the POSITION ERROR voltage stays at +5VDC.
If the motor gets ahead of the STEP pulses such as during very rapid
deceleration, the voltage will decrease by 0.04 volts for every encoder count
the motor is ahead of the STEP pulses sent. The PID algorithm will force the
motor to match the STEP input over time and restore the POSITION ERROR voltage
back to +5 VDC.

GAIN AND DAMPING:

GAIN and DAMPING settings
generally track each other. If you increase GAIN (greater stiffness), then
increased DAMPING is needed as well to restore critical damping. Be careful,
increasing GAIN without increasing DAMPING may cause the motor to break out into
violent oscillation.

The higher GAIN is set, the noisier the motor will
be when stopped. This is because higher gain causes more vigorous dithering
between encoder counts at rest. There is a trade-off between high gain (high
stiffness) on one hand and excessive dithering (noise and motor heating) on the
other. Use your best judgment here.

To see how your servo is compensated,
it is first necessary to induce a disturbance. The easiest way is to switch the
DIRECTION input while commanding a constant speed via the STEP input. The abrupt
direction change puts just the momentary load needed on the motor while you
watch how it responds.

If you are using an oscilloscope, use channel 1 on
the test point and channel 2 on the DIRECTION input. Set the trigger to
“normal”, trigger source to channel 2 and trigger edge to “+”. You should see a
single sweep for every clockwise change in direction.

Slowly increase
STEP speed until you get a picture similar to one of the three above, and then
do the following:

1) OVERDAMPED: Decrease DAMPING or increase GAIN
2)
CRITICALLY DAMPED: Do nothing; you’re there
3) UNDERDAMPED: Decrease GAIN or
increase DAMPING

CURRENT LIMIT:

The current LIMIT trimpot sets
maximum current the motor is permitted to have. It is adjustable from 0 amps to
20 amps. Normally the LIMIT trimpot is set to maximum (20 amps) unless you want
to limit motor torque to a lower value.

Motor speed and position is
unaffected by the current LIMIT setting unless the torque demand due to load
exceeds this setting, then the motor position will fall behind the command
position because of insufficient torque.

FAULT INDICATOR:

The
FAULT indicator is on while the drive is in power-on reset, the DISABLE input is
held “low” or if the protection circuit is tripped due to a fault condition. All
power MOSFETs are turned off and all internal counters are reset. The FAULT
condition lasts for 3 seconds, and then self-resets to try again. If the
protection circuit tripped it and the cause is not cleared, then it will
immediately re-enter the FAULT state again and repeat the cycle.

There
are two conditions that will trip the protection circuit. One condition is if a
short-circuit occurs and current exceeds 20 amps.

The other condition is
if the POSITION ERROR exceeds +/- 128 counts causing a break of the servo-lock.
This condition can have several causes:

1) The loop settings are severely
under-damped and the motor breaks out into oscillation.
2) Excessive motor
load due to acceleration or workload.
3) The speed command in excess of what
the motor can deliver.
4) The current LIMIT is set too low.
5) The power
supply current is insufficient for the demand.
6) The motor is wired
backwards, is broken or disconnected.
7) Encoder failure.

REVERSING
DEFAULT MOTOR DIRECTION:

The G320 will turn the motor in the CW direction
when the DIRECTION input is “high” (logical “1”, or +5VDC). If instead CCW is
preferred, then:

1) Reverse the motor “+” and “-“ leads (TERMINAL 3 with
TERMINAL 4)
2) Reverse the encoder “channel A” and “channel B” leads
(TERMINAL 8 with TERMINAL 9)

TERMINAL 5 ERR /
RES

This terminal functions as an ERROR output and as a RESET input.
Because this terminal functions as both an input and an output, some detailed
description is necessary.

When first testing the G320, ERR/RES (term. 5)
was connected to ENC+ (term. 7). It can be left that way if it is not necessary
to read the state of the ERROR output. Otherwise, the following details are
important.

The ERROR output is latched in the “ERROR” state (term. 5 =
“0”) by the power-on reset circuitry in the G320. It will stay in this state
indefinitely until it is cleared by applying +5V to this terminal for at least 5
seconds.

The voltage on this terminal is +5VDC when the G320 is
functioning normally. The voltage on this terminal goes to 0VDC whenever the
FAULT indicator is lit. This output can be used to signal your controller that
an error has occurred.

The
above circuit shows how to implement an external switch to clear an ERROR
condition and RESET the G320, while still being able to read the state of the
drive. It also includes an optional FAULT LED circuit if a remote indication of
the state of the G320 is desired.

Normally when the G320 is first powered
up, it will be necessary to push the momentary switch to START for 5 seconds.
This will clear the power-on reset condition and extinguish the FAULT LED. The
motor will then be enabled and the drive will begin to operate.

If at
anytime after that a condition occurs that causes the G320 to “fault out”, such
as not being able to complete a step command, the ERR/RES terminal will go to
“0”, signaling the computer an error has occurred. This will require the
operator to correct the problem that caused the fault and then push the switch
to “START” for 5 seconds to re-enable the G320.

At anytime the operator
can push the switch to the “STOP” position to immediately halt the G320 drive.
Anytime the G320 is in the “FAULT” state (FAULT LED lit), all switching action
stops and the motor freewheels and is unpowered. This will light the “FAULT”
light.

G320
SPECIFICATIONS:

Power Supply:
18
to 80 VDC
Motor Current:
0 to 20
Amps
Lock Range:
+/-
128 count following error
Feedback:

Quadrature TTL Encoder
Feedback Resolution:
X4 Encoder Line
Count
Switching Frequency:
25 kHz
Current Limit:

0 to 20 Amp, Trimpot Adjustable
Analog PID:

Damping and Gain Trimpots
Step
Pulse Frequency:
0 to 250 kHz
Step Pulse “0” Time:
0.5 Microseconds Min.
Step Pulse “1” Time:
3.5
Microseconds Min.
Temperature Range:
0 to 70C
Humidity:

Up to 95% (non
condensing)
Size:

2.5" X 2.5” X 0.825"
Weight:

3.6
oz weight
Encoder Supply:
+5VDC, 50 mA max

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