CNC Controller Update: Servo Motor Question

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atgordon
Posts: 2
Joined: Sat Sep 28, 2013 9:43 am

CNC Controller Update: Servo Motor Question

Post by atgordon » Fri Mar 25, 2016 2:57 pm

I have a late 90's Clausing Kondia FV1-CNC with Delta 20 controller. It is working OK, but it has gone through two servo boards, a controller board and a power supply. Good news is that there are only 5 more boards that can go wrong!

The iron and servos are great condition (the mill was used in a prototyping lab), so it is a great candidate for MACH3 or LinuxCNC update. I would like to reuse the servos but I'm having some difficulty in working out how to wire the encoders ...

The mill is fitted with Baldor MT-4070 x 2 and MT-4090 x 1 DC servo motors (80v max, 9a max). The motors are fitted with tach and encoder connections.

The connection schematic shows:
PIN
A Channel A
B Channel A-
C Channel B
D Channel B-
E Channel Z
F Channel Z-
G Motor Ground
H +5V DC
I Common
J NC
K Encoder shield
L Tach Shield
M Tach lead +
N Motor Lead -
O Tach lead -
P Motor Lead +

I have looked at both the Gecko G320X servo drive and the CNCdrive DG4S series, but cannot work out the relationship between the encoder input and my outputs, see below for the DG4S connection schema:

CONNECTOR 1
1. Ground
2. 5Volts (output from the drive to the encoder)
3. NC (Do not connect)
4. NC (Do not connect)
5. A+ signal input
6. A- signal input 7.
B+ signal input 8.
B- signal input
CONNECTOR 2

1. Step signal input
2. Direction signal input
3. Ground for Step and Direction signals (NOT for power)
4. 5V power input. (if this input is fed then the 7.pin should not be connected!)
5. Reset (input) and Stop input)
6. Error (output) and Stop input
7. DC power + (12V DC input for digital processor)
8. DC power – (ground for the 12V DC power supply)

The Z Z- connections have to go somewhere, don't they? Are they linked to the STEP and DIR connections?

Has anyone successfully wired existing servo motors/encoders to modern servo drives, if yes, help much appreciated! :?: :?:

choprboy
Posts: 202
Joined: Sat Oct 29, 2011 11:23 pm

Re: CNC Controller Update: Servo Motor Question

Post by choprboy » Sat Mar 26, 2016 1:11 am

Z+/Z- is typically an index signal, one pulse crossing the zero point of each full servo rotation. It helps to find a consistent home point (i.e. home zero is 150 +/-15 pulses from the limit switch, where Z triggers) and detect missed A/B pulses, but is not necessarily required.

atgordon
Posts: 2
Joined: Sat Sep 28, 2013 9:43 am

Re: CNC Controller Update: Servo Motor Question

Post by atgordon » Sat Mar 26, 2016 10:59 am

choprboy wrote:Z+/Z- is typically an index signal, one pulse crossing the zero point of each full servo rotation. It helps to find a consistent home point (i.e. home zero is 150 +/-15 pulses from the limit switch, where Z triggers) and detect missed A/B pulses, but is not necessarily required.
Many thanks. I had seen a TTL output that confirms your read on it. I had a feeling that it could be ignored since it is "belt and braces" when using a limit switch.

Still no closer on what to do with the STEP and DIRECTION inputs: any idea where they are derived from the servo motor/encoder?

choprboy
Posts: 202
Joined: Sat Oct 29, 2011 11:23 pm

Re: CNC Controller Update: Servo Motor Question

Post by choprboy » Sat Mar 26, 2016 1:51 pm

Step and Direction come from your program controller, to the servo driver, not the encoder. Your controller sets direction and sends 10 pulses on step to tell the driver to move 10 steps. The driver applies voltage polarity to drive the motor in the correct direction and confirms direction/measures movement using the quadrature encoder output (A/B), turning off power when the correct position is attained.

hanermo
Posts: 42
Joined: Tue Oct 01, 2013 5:47 am

Re: CNC Controller Update: Servo Motor Question

Post by hanermo » Sat Mar 26, 2016 2:28 pm

No problem, very easy.
Just use *modern* brushless servo drives with differential wiring.

I always imported the drive and motors as packages, so no experience mix and matching.

Wiring a modern differential stepper drive to a stepper, is also easy.
Going from a differential drive , ie A, A/ to a single ended motor, is also easy.
There are 2 schemes, and one or both will work.

The z is index, as noted.

I would use a modern drive.
All my 16+ geckos are retired, and I now use better stuff.

Modern drives:
No hiss, stutter, anti-jitter circuitry, on servos. Very important.
Soft start. Very important.
No back-emf startup. Extremely important.
Differential wiring. Important.
Less noise: Important.
Less heat: Important.
Disable signal. Important (works fine on g251, 203V, G320, but not on integrated packages like G540).
Brushless (sevro). Extremely important.

All above 7 features are lacking on gecko products.

You will need a hw motion-control card.
CSlabs csmio, if you can afford one, or pokeys cncaddon, are the best choices, for mach4(mach3).
Mesa for linuxcnc.

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Bill Shields
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Re: CNC Controller Update: Servo Motor Question

Post by Bill Shields » Thu May 12, 2016 9:27 pm

suggest that you not ignore the Z+ if you have a way to handle it.

suggestion from industrial practice to ensure repeatability:

In your 'find zero function':

check that the switch is open
drive to the limit switch until it closes
back off until it opens
continue in same direction until you hit the Z+ pulse
call it zero.

greenbuggy
Posts: 5
Joined: Tue Oct 28, 2014 12:38 am

Re: CNC Controller Update: Servo Motor Question

Post by greenbuggy » Thu Jun 16, 2016 12:07 am

Do your motors say 90V max on them?

I ask because my Lagun uses Baldor MTE-4070's and they're good for 150ish volts. Higher voltages may exclude the use of Gecko drives but will get you faster acceleration and rapid speeds.

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