Re: [Emc-users] Dual servo motor gantry

[rayj]

Dave,

Thanks for the clarification, and the education.

I'm strictly a hobbyist, with a box full of NEMA 34 stepper motors. 
Anytime steppers are mentioned, I pay attention.  Obviously, the size of 
the motors limits my design options, hence my interest in using 2 together.

I saw you were using stepper motor signals and incorrectly assumed you 
were using stepper motors.

Thanks again for the informative reply.

Raymond Julian
Kettle River, MN

The things we admire in men, kindness and generosity, openness, honesty, 
understanding and feeling are the concomitants of failure in our system. 
And those traits we detest, sharpness, greed, acquisitiveness, meanness, 
egotism and self-interest are the traits of success. And while men 
admire the quality of the first they love the produce of the second. 
-John Steinbeck, novelist, Nobel laureate (1902-1968)

On 01/10/2015 10:49 AM, Dave Cole wrote:
> No..  the Automation Direct servo drives are full blown digital servo
> drives.
>
> They can operate in at least three different modes.   Position mode (the
> drive accepts step and direction signals from the CNC controller),
> Velocity mode (the CNC controller outputs a +/-10 volt signal that is a
> velocity command signal - ie how fast do you want the motor to rotate in
> forward or reverse direction), and torque mode (the CNC controller
> outputs a +/- 10 volt signal that is a torque command - how much torque
> should the motor output to the system.).
>
> LinuxCNC can output a step and direction signal which is oftentimes used
> to control stepper motors, but can also be used to control smart servo
> drives that can accept a step and direction signal (like a stepper
> drive).   In the case of a smart servo drive, the drive itself closes
> the position loop itself by receiving the encoder signal from the motors.
> LinuxCNC is also frequently used with servo drives in velocity mode.  In
> that case LinuxCNC outputs a +/-10 volt signal which indicates a
> velocity command to the drive (how fast and in a positive or negative
> direction).I believe that LinuxCNC can also drive servos in Torque
> mode but torque mode is trickier to tune, and I have never used that
> with LinuxCNC.   (I don't see any advantage of using torque mode with
> LinuxCNC for most applications.)
>
> So in the situation we are discussing, the smart servo drives are doing
> their own closed loop position control and the CNC controller just sends
> a step and direction pulse to them to rotate in the positive and
> negative direction and at a speed dictated by the the pulse stream
> rate. The drives themselves receive the encoder feedback pulses and
> also the step and direction pulses from the CNC controller so the drives
> themselves knows where they are suppose to be (via the position command
> from the LinuxCNC controller) and where they actually are (from the
> motor encoder).The difference is the following error.   If the
> following error becomes excessive the drives themselves are intelligent
> enough to shut themselves down.When they do that they usually output
> a fault signal.   That fault signal can be wired to the opposite servo
> drive as a shutdown signal.   So if either drive has excessive following
> error (like something has jammed up) then both gantry drives will
> shutdown preventing the gantry from becoming racked out of shape.
>
> In the particular case of the gantry machine I did a few years ago, I
> also had a PLC in the system.   So I wired the servo drives into the
> PLC.   If either servo drive output a fault signal, I shutdown the
> opposite servo drive.But I only did that because I had a PLC in the
> system.   I could have cross wired the servo drives directly (it might
> have required a relay) to make the logical connection.
>
> This is the servo drive and motor I used for that machine.
> http://www.automationdirect.com/adc/Shopping/Catalog/Motion_Control/Servo_Systems/Medium_Inertia_%281KW_-_3KW%29_Servo_Systems/1KW_Servo_System_%28Med_Inertia%29
>
>
> Machmotion.com sells Teco servo drives (as do a few other distributors
> in the USA) and they work almost identically to the Automation Direct
> drives but cost about 30% less.
>
> Dave
>
>
> On 1/9/2015 5:08 PM, rayj wrote:
>> Dave,
>>
>> Thanks for the reply.
>>
>> So you have position feedback from the motor shafts, essentially a servo
>> system with stepper motors, kinda?  And if the detected position differs
>> from commanded position by a specified amount, it stops?
>>
>> Did the motors come with the feedback hardware or did you add it?  If
>> you added it, what hardware did you use?
>>
>>
>> Raymond Julian
>> Kettle River, MN
>>
>> The things we admire in men, kindness and generosity, openness, honesty,
>> understanding and feeling are the concomitants of failure in our system.
>> And those traits we detest, sharpness, greed, acquisitiveness, meanness,
>> egotism and self-interest are the traits of success. And while men
>> admire the quality 

Re: [Emc-users] Dual servo motor gantry

[Dave Cole]

No..  the Automation Direct servo drives are full blown digital servo 
drives.

They can operate in at least three different modes.   Position mode (the 
drive accepts step and direction signals from the CNC controller), 
Velocity mode (the CNC controller outputs a +/-10 volt signal that is a 
velocity command signal - ie how fast do you want the motor to rotate in 
forward or reverse direction), and torque mode (the CNC controller 
outputs a +/- 10 volt signal that is a torque command - how much torque 
should the motor output to the system.).

LinuxCNC can output a step and direction signal which is oftentimes used 
to control stepper motors, but can also be used to control smart servo 
drives that can accept a step and direction signal (like a stepper 
drive).   In the case of a smart servo drive, the drive itself closes 
the position loop itself by receiving the encoder signal from the motors.
LinuxCNC is also frequently used with servo drives in velocity mode.  In 
that case LinuxCNC outputs a +/-10 volt signal which indicates a 
velocity command to the drive (how fast and in a positive or negative 
direction).I believe that LinuxCNC can also drive servos in Torque 
mode but torque mode is trickier to tune, and I have never used that 
with LinuxCNC.   (I don't see any advantage of using torque mode with 
LinuxCNC for most applications.)

So in the situation we are discussing, the smart servo drives are doing 
their own closed loop position control and the CNC controller just sends 
a step and direction pulse to them to rotate in the positive and 
negative direction and at a speed dictated by the the pulse stream 
rate. The drives themselves receive the encoder feedback pulses and 
also the step and direction pulses from the CNC controller so the drives 
themselves knows where they are suppose to be (via the position command 
from the LinuxCNC controller) and where they actually are (from the 
motor encoder).The difference is the following error.   If the 
following error becomes excessive the drives themselves are intelligent 
enough to shut themselves down.When they do that they usually output 
a fault signal.   That fault signal can be wired to the opposite servo 
drive as a shutdown signal.   So if either drive has excessive following 
error (like something has jammed up) then both gantry drives will 
shutdown preventing the gantry from becoming racked out of shape.

In the particular case of the gantry machine I did a few years ago, I 
also had a PLC in the system.   So I wired the servo drives into the 
PLC.   If either servo drive output a fault signal, I shutdown the 
opposite servo drive.But I only did that because I had a PLC in the 
system.   I could have cross wired the servo drives directly (it might 
have required a relay) to make the logical connection.

This is the servo drive and motor I used for that machine.
http://www.automationdirect.com/adc/Shopping/Catalog/Motion_Control/Servo_Systems/Medium_Inertia_%281KW_-_3KW%29_Servo_Systems/1KW_Servo_System_%28Med_Inertia%29
 


Machmotion.com sells Teco servo drives (as do a few other distributors 
in the USA) and they work almost identically to the Automation Direct 
drives but cost about 30% less.

Dave


On 1/9/2015 5:08 PM, rayj wrote:
> Dave,
>
> Thanks for the reply.
>
> So you have position feedback from the motor shafts, essentially a servo
> system with stepper motors, kinda?  And if the detected position differs
> from commanded position by a specified amount, it stops?
>
> Did the motors come with the feedback hardware or did you add it?  If
> you added it, what hardware did you use?
>
>
> Raymond Julian
> Kettle River, MN
>
> The things we admire in men, kindness and generosity, openness, honesty,
> understanding and feeling are the concomitants of failure in our system.
> And those traits we detest, sharpness, greed, acquisitiveness, meanness,
> egotism and self-interest are the traits of success. And while men
> admire the quality of the first they love the produce of the second.
> -John Steinbeck, novelist, Nobel laureate (1902-1968)
>
> On 01/09/2015 03:40 PM, Dave Cole wrote:
>> Hi Raymond,
>>
>> I used Automation Direct servo drives on that job and they can be setup
>> to shutdown on excessive following error.  (Deviation from the step and
>> direction commanded position).They can also be shutdown by an
>> external input.So if you cross wire the drives so if one shuts down
>> on following error, it shuts down the other drive and visa versa, it
>> becomes a self protecting system.   If either drive has excessive
>> following error it kills itself and also the other drive.That
>> prevents the gantry from being racked out of position if something goes
>> wrong.
>>
>> A common reset wired to both drives can also bring them back to life
>> after a shutdown.
>>
>> It works well and is quite simple once it is implemented.
>>
>> Dave
>>
>> On 1/9/2015 4:03 PM, rayj wrote:
>>> Greetings Dave,
>>>
>>>

Re: [Emc-users] Dual servo motor gantry

[rayj]

Dave,

Thanks for the reply.

So you have position feedback from the motor shafts, essentially a servo 
system with stepper motors, kinda?  And if the detected position differs 
from commanded position by a specified amount, it stops?

Did the motors come with the feedback hardware or did you add it?  If 
you added it, what hardware did you use?


Raymond Julian
Kettle River, MN

The things we admire in men, kindness and generosity, openness, honesty, 
understanding and feeling are the concomitants of failure in our system. 
And those traits we detest, sharpness, greed, acquisitiveness, meanness, 
egotism and self-interest are the traits of success. And while men 
admire the quality of the first they love the produce of the second. 
-John Steinbeck, novelist, Nobel laureate (1902-1968)

On 01/09/2015 03:40 PM, Dave Cole wrote:
> Hi Raymond,
>
> I used Automation Direct servo drives on that job and they can be setup
> to shutdown on excessive following error.  (Deviation from the step and
> direction commanded position).They can also be shutdown by an
> external input.So if you cross wire the drives so if one shuts down
> on following error, it shuts down the other drive and visa versa, it
> becomes a self protecting system.   If either drive has excessive
> following error it kills itself and also the other drive.That
> prevents the gantry from being racked out of position if something goes
> wrong.
>
> A common reset wired to both drives can also bring them back to life
> after a shutdown.
>
> It works well and is quite simple once it is implemented.
>
> Dave
>
> On 1/9/2015 4:03 PM, rayj wrote:
>> Greetings Dave,
>>
>> I have some long term plans to build a gantry similar to the one you
>> describe.
>>
>> When you say it kicks out the controls, I'm not sure what you mean. Is
>> there some physical safeguard, like a detent or or clutch, or is it
>> something in the software you're talking about.
>>
>> TIA
>>
>> Raymond Julian
>> Kettle River, MN
>>
>> The things we admire in men, kindness and generosity, openness, honesty,
>> understanding and feeling are the concomitants of failure in our system.
>> And those traits we detest, sharpness, greed, acquisitiveness, meanness,
>> egotism and self-interest are the traits of success. And while men
>> admire the quality of the first they love the produce of the second.
>> -John Steinbeck, novelist, Nobel laureate (1902-1968)
>>
>> On 01/09/2015 10:47 AM, Dave Cole wrote:
>>> I did one of these several years ago. The machine has 1 KW servos on
>>> each end of the gantry driving ball screws.The gantry was quite
>>> rigid so when the power was removed it self squared.   There was one one
>>> home switch.  I ended up using servo drives in step and direction
>>> mode and fed them with a pulse train from LinuxCNC.   That worked out
>>> fine.  I fed the same step and direction signal to each gantry drive.
>>> If there is any significant following error on either drive, it kicks
>>> out the controls so the gantry cannot become racked out of shape.
>>> It has been running like that now for over 3 years with no issues and
>>> the machine runs up to about 700 ipm.  The machine runs every day,
>>> sometimes two shifts per day.
>>> I considered doing two separate closed loop axes back to the PC, but I
>>> thought it would be easier to try the step and direction approach
>>> first.   That worked, so I stuck with it.
>>> No regrets on that decision.
>>>
>>> Dave
>>>
>>> On 1/9/2015 10:57 AM, Eric H. Johnson wrote:
 Hi all,



 I am looking to do an upgrade on a large XY table where the gantry is 
 driven
 by to oppositely mounted servo motors. Both sets of encoders run back to 
 the
 existing controller. Can I just give a generous deadband to the slave axis,
 or is there a better way to address this configuration so the motors don't
 fight each other. I believe it uses a single home switch which can then be
 fed to both axes for purposes of homing. Anyone done this? Anything else to
 look out for?



 Thanks,

 Eric




 
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Re: [Emc-users] Dual servo motor gantry

[Dave Cole]

Hi Raymond,

I used Automation Direct servo drives on that job and they can be setup 
to shutdown on excessive following error.  (Deviation from the step and 
direction commanded position).They can also be shutdown by an 
external input.So if you cross wire the drives so if one shuts down 
on following error, it shuts down the other drive and visa versa, it 
becomes a self protecting system.   If either drive has excessive 
following error it kills itself and also the other drive.That 
prevents the gantry from being racked out of position if something goes 
wrong.

A common reset wired to both drives can also bring them back to life 
after a shutdown.

It works well and is quite simple once it is implemented.

Dave

On 1/9/2015 4:03 PM, rayj wrote:
> Greetings Dave,
>
> I have some long term plans to build a gantry similar to the one you
> describe.
>
> When you say it kicks out the controls, I'm not sure what you mean. Is
> there some physical safeguard, like a detent or or clutch, or is it
> something in the software you're talking about.
>
> TIA
>
> Raymond Julian
> Kettle River, MN
>
> The things we admire in men, kindness and generosity, openness, honesty,
> understanding and feeling are the concomitants of failure in our system.
> And those traits we detest, sharpness, greed, acquisitiveness, meanness,
> egotism and self-interest are the traits of success. And while men
> admire the quality of the first they love the produce of the second.
> -John Steinbeck, novelist, Nobel laureate (1902-1968)
>
> On 01/09/2015 10:47 AM, Dave Cole wrote:
>> I did one of these several years ago. The machine has 1 KW servos on
>> each end of the gantry driving ball screws.The gantry was quite
>> rigid so when the power was removed it self squared.   There was one one
>> home switch.  I ended up using servo drives in step and direction
>> mode and fed them with a pulse train from LinuxCNC.   That worked out
>> fine.  I fed the same step and direction signal to each gantry drive.
>> If there is any significant following error on either drive, it kicks
>> out the controls so the gantry cannot become racked out of shape.
>> It has been running like that now for over 3 years with no issues and
>> the machine runs up to about 700 ipm.  The machine runs every day,
>> sometimes two shifts per day.
>> I considered doing two separate closed loop axes back to the PC, but I
>> thought it would be easier to try the step and direction approach
>> first.   That worked, so I stuck with it.
>> No regrets on that decision.
>>
>> Dave
>>
>> On 1/9/2015 10:57 AM, Eric H. Johnson wrote:
>>> Hi all,
>>>
>>>
>>>
>>> I am looking to do an upgrade on a large XY table where the gantry is driven
>>> by to oppositely mounted servo motors. Both sets of encoders run back to the
>>> existing controller. Can I just give a generous deadband to the slave axis,
>>> or is there a better way to address this configuration so the motors don't
>>> fight each other. I believe it uses a single home switch which can then be
>>> fed to both axes for purposes of homing. Anyone done this? Anything else to
>>> look out for?
>>>
>>>
>>>
>>> Thanks,
>>>
>>> Eric
>>>
>>>
>>>
>>>
>>> >> 7fcnk8RJ6s6N8rBF7Rd3_yKW18Chwm1k1H6H0?si=6453247850577920&pi=8828d77849c9460
>>> b95fcaf96870fbe9d>
>>> --
>>> Dive into the World of Parallel Programming! The Go Parallel Website,
>>> sponsored by Intel and developed in partnership with Slashdot Media, is your
>>> hub for all things parallel software development, from weekly thought
>>> leadership blogs to news, videos, case studies, tutorials and more. Take a
>>> look and join the conversation now. http://goparallel.sourceforge.net
>>> ___
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>>> https://lists.sourceforge.net/lists/listinfo/emc-users
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>>
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>> hub for all things parallel software development, from weekly thought
>> leadership blogs to news, videos, case studies, tutorials and more. Take a
>> look and join the conversation now. http://goparallel.sourceforge.net
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> hub 

Re: [Emc-users] Dual servo motor gantry

[Dave Cole]

On 1/9/2015 3:30 PM, andy pugh wrote:
> On 9 January 2015 at 20:09, Eric H. Johnson  wrote:
>> I do not think I have that option, at least not without changing amplifiers.
>> The only interface to the existing amplifiers is a -10 to 10V signal. This
>> configuration with stepper motors is pretty much falling off a log easy.
> It shouldn't be horribly hard with servos, as long as the motors are
> in control at all times.
>
> The danger is runaway during the tuning phase. I think it might be
> wise to set up something in HAL that kills the system if the two
> encoders differ in value by more than a small amount.

I agree with Andy.   Doing it with servos should not be hard if your 
gantry self squares.   (IE, when power is off the gantry is adequately 
square).
So then you enable the servos, the motors are both at 0 position and you 
can go from there.

If your encoder feedback position differs between motors, shutdown the 
motors.

If the drives are digital and you can tune them with the same exact 
tuning numbers this should not be too difficult.   If you have analog 
drives, it might get "interesting"
trying to match the drive tuning so you don't trip out on encoder 
differences (position deviation from side to side).

Dave

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Re: [Emc-users] Dual servo motor gantry

[rayj]

Greetings Dave,

I have some long term plans to build a gantry similar to the one you 
describe.

When you say it kicks out the controls, I'm not sure what you mean. Is 
there some physical safeguard, like a detent or or clutch, or is it 
something in the software you're talking about.

TIA

Raymond Julian
Kettle River, MN

The things we admire in men, kindness and generosity, openness, honesty, 
understanding and feeling are the concomitants of failure in our system. 
And those traits we detest, sharpness, greed, acquisitiveness, meanness, 
egotism and self-interest are the traits of success. And while men 
admire the quality of the first they love the produce of the second. 
-John Steinbeck, novelist, Nobel laureate (1902-1968)

On 01/09/2015 10:47 AM, Dave Cole wrote:
> I did one of these several years ago. The machine has 1 KW servos on
> each end of the gantry driving ball screws.The gantry was quite
> rigid so when the power was removed it self squared.   There was one one
> home switch.  I ended up using servo drives in step and direction
> mode and fed them with a pulse train from LinuxCNC.   That worked out
> fine.  I fed the same step and direction signal to each gantry drive.
> If there is any significant following error on either drive, it kicks
> out the controls so the gantry cannot become racked out of shape.
> It has been running like that now for over 3 years with no issues and
> the machine runs up to about 700 ipm.  The machine runs every day,
> sometimes two shifts per day.
> I considered doing two separate closed loop axes back to the PC, but I
> thought it would be easier to try the step and direction approach
> first.   That worked, so I stuck with it.
> No regrets on that decision.
>
> Dave
>
> On 1/9/2015 10:57 AM, Eric H. Johnson wrote:
>> Hi all,
>>
>>
>>
>> I am looking to do an upgrade on a large XY table where the gantry is driven
>> by to oppositely mounted servo motors. Both sets of encoders run back to the
>> existing controller. Can I just give a generous deadband to the slave axis,
>> or is there a better way to address this configuration so the motors don't
>> fight each other. I believe it uses a single home switch which can then be
>> fed to both axes for purposes of homing. Anyone done this? Anything else to
>> look out for?
>>
>>
>>
>> Thanks,
>>
>> Eric
>>
>>
>>
>>
>> > 7fcnk8RJ6s6N8rBF7Rd3_yKW18Chwm1k1H6H0?si=6453247850577920&pi=8828d77849c9460
>> b95fcaf96870fbe9d>
>> --
>> Dive into the World of Parallel Programming! The Go Parallel Website,
>> sponsored by Intel and developed in partnership with Slashdot Media, is your
>> hub for all things parallel software development, from weekly thought
>> leadership blogs to news, videos, case studies, tutorials and more. Take a
>> look and join the conversation now. http://goparallel.sourceforge.net
>> ___
>> Emc-users mailing list
>> Emc-users@lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/emc-users
>
> ---
> This email has been checked for viruses by Avast antivirus software.
> http://www.avast.com
>
>
> --
> Dive into the World of Parallel Programming! The Go Parallel Website,
> sponsored by Intel and developed in partnership with Slashdot Media, is your
> hub for all things parallel software development, from weekly thought
> leadership blogs to news, videos, case studies, tutorials and more. Take a
> look and join the conversation now. http://goparallel.sourceforge.net
> ___
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Re: [Emc-users] Dual servo motor gantry

[andy pugh]

On 9 January 2015 at 20:09, Eric H. Johnson  wrote:
> I do not think I have that option, at least not without changing amplifiers.
> The only interface to the existing amplifiers is a -10 to 10V signal. This
> configuration with stepper motors is pretty much falling off a log easy.

It shouldn't be horribly hard with servos, as long as the motors are
in control at all times.

The danger is runaway during the tuning phase. I think it might be
wise to set up something in HAL that kills the system if the two
encoders differ in value by more than a small amount.

-- 
atp
If you can't fix it, you don't own it.
http://www.ifixit.com/Manifesto

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Re: [Emc-users] Dual servo motor gantry

[Eric H. Johnson]

Dave,

I do not think I have that option, at least not without changing amplifiers.
The only interface to the existing amplifiers is a -10 to 10V signal. This
configuration with stepper motors is pretty much falling off a log easy. I
have a 4' x 8' stepper table configured exactly that way.

Thanks,
Eric


I did one of these several years ago. The machine has 1 KW servos on 
each end of the gantry driving ball screws.The gantry was quite 
rigid so when the power was removed it self squared.   There was one one 
home switch.  I ended up using servo drives in step and direction 
mode and fed them with a pulse train from LinuxCNC.   That worked out 
fine.  I fed the same step and direction signal to each gantry drive.   
If there is any significant following error on either drive, it kicks out
the controls so the gantry cannot become racked out of shape.
It has been running like that now for over 3 years with no issues and the
machine runs up to about 700 ipm.  The machine runs every day, sometimes two
shifts per day.
I considered doing two separate closed loop axes back to the PC, but I
thought it would be easier to try the step and direction approach 
first.   That worked, so I stuck with it.
No regrets on that decision.

Dave

On 1/9/2015 10:57 AM, Eric H. Johnson wrote:
> Hi all,
>
>   
>
> I am looking to do an upgrade on a large XY table where the gantry is 
> driven by to oppositely mounted servo motors. Both sets of encoders 
> run back to the existing controller. Can I just give a generous 
> deadband to the slave axis, or is there a better way to address this 
> configuration so the motors don't fight each other. I believe it uses 
> a single home switch which can then be fed to both axes for purposes 
> of homing. Anyone done this? Anything else to look out for?
>
>   
>
> Thanks,
>
> Eric
>
>   
>
>   
>  4LCQRN
> 7fcnk8RJ6s6N8rBF7Rd3_yKW18Chwm1k1H6H0?si=6453247850577920&pi=8828d7784
> 9c9460
> b95fcaf96870fbe9d>
> --
>  Dive into the World of Parallel Programming! The Go Parallel 
> Website, sponsored by Intel and developed in partnership with Slashdot 
> Media, is your hub for all things parallel software development, from 
> weekly thought leadership blogs to news, videos, case studies, 
> tutorials and more. Take a look and join the conversation now. 
> http://goparallel.sourceforge.net 
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Re: [Emc-users] Dual servo motor gantry

[Eric H. Johnson]

Viesturs,

It might add some positioning error, but I am thinking of something on the
order of a couple hundredths of an inch or less. The application is an
ultrasonic knife cutting table, so with the flex of the blade I can
certainly tolerate a couple hundredths of an inch error on one side of the
gantry. The motors and amplifiers are identical, so performance should be
very close to identical as well.

I do not see two home switches as viable, it is a prox switch, so precisely
aligning the field effect of two such switches would be a nightmare, not to
mention how easily one could get knocked out of alignment. 

Thanks,
Eric 

Correct me, if I am wrong, but AFAIK adding deadband will added also in the
positioning precision by definition, I seriously doubt that it is
acceptable.
Any reason not to add another homeswitch, so that each of those joints has
one and treat it as a normal gantry machine?



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Re: [Emc-users] Dual servo motor gantry

[Todd Zuercher]

I could see a single home switch being advantageous combined with home to 
index. 

- Original Message -
From: "Viesturs Lācis" 
To: "Enhanced Machine Controller (EMC)" 
Sent: Friday, January 9, 2015 11:45:06 AM
Subject: Re: [Emc-users] Dual servo motor gantry

2015-01-09 17:57 GMT+02:00 Eric H. Johnson :
> Hi all,
>
>
>
> I am looking to do an upgrade on a large XY table where the gantry is driven
> by to oppositely mounted servo motors. Both sets of encoders run back to the
> existing controller. Can I just give a generous deadband to the slave axis,
> or is there a better way to address this configuration so the motors don't
> fight each other. I believe it uses a single home switch which can then be
> fed to both axes for purposes of homing. Anyone done this? Anything else to
> look out for?
>

Correct me, if I am wrong, but AFAIK adding deadband will added also
in the positioning precision by definition, I seriously doubt that it
is acceptable.
Any reason not to add another homeswitch, so that each of those joints
has one and treat it as a normal gantry machine?

Viesturs

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Re: [Emc-users] Dual servo motor gantry

[Dave Cole]

I did one of these several years ago. The machine has 1 KW servos on 
each end of the gantry driving ball screws.The gantry was quite 
rigid so when the power was removed it self squared.   There was one one 
home switch.  I ended up using servo drives in step and direction 
mode and fed them with a pulse train from LinuxCNC.   That worked out 
fine.  I fed the same step and direction signal to each gantry drive.   
If there is any significant following error on either drive, it kicks 
out the controls so the gantry cannot become racked out of shape.
It has been running like that now for over 3 years with no issues and 
the machine runs up to about 700 ipm.  The machine runs every day, 
sometimes two shifts per day.
I considered doing two separate closed loop axes back to the PC, but I 
thought it would be easier to try the step and direction approach 
first.   That worked, so I stuck with it.
No regrets on that decision.

Dave

On 1/9/2015 10:57 AM, Eric H. Johnson wrote:
> Hi all,
>
>   
>
> I am looking to do an upgrade on a large XY table where the gantry is driven
> by to oppositely mounted servo motors. Both sets of encoders run back to the
> existing controller. Can I just give a generous deadband to the slave axis,
> or is there a better way to address this configuration so the motors don't
> fight each other. I believe it uses a single home switch which can then be
> fed to both axes for purposes of homing. Anyone done this? Anything else to
> look out for?
>
>   
>
> Thanks,
>
> Eric
>
>   
>
>   
>  7fcnk8RJ6s6N8rBF7Rd3_yKW18Chwm1k1H6H0?si=6453247850577920&pi=8828d77849c9460
> b95fcaf96870fbe9d>
> --
> Dive into the World of Parallel Programming! The Go Parallel Website,
> sponsored by Intel and developed in partnership with Slashdot Media, is your
> hub for all things parallel software development, from weekly thought
> leadership blogs to news, videos, case studies, tutorials and more. Take a
> look and join the conversation now. http://goparallel.sourceforge.net
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Re: [Emc-users] Dual servo motor gantry

[Viesturs Lācis]

2015-01-09 17:57 GMT+02:00 Eric H. Johnson :
> Hi all,
>
>
>
> I am looking to do an upgrade on a large XY table where the gantry is driven
> by to oppositely mounted servo motors. Both sets of encoders run back to the
> existing controller. Can I just give a generous deadband to the slave axis,
> or is there a better way to address this configuration so the motors don't
> fight each other. I believe it uses a single home switch which can then be
> fed to both axes for purposes of homing. Anyone done this? Anything else to
> look out for?
>

Correct me, if I am wrong, but AFAIK adding deadband will added also
in the positioning precision by definition, I seriously doubt that it
is acceptable.
Any reason not to add another homeswitch, so that each of those joints
has one and treat it as a normal gantry machine?

Viesturs

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[Emc-users] Dual servo motor gantry

[Eric H. Johnson]

Hi all,

 

I am looking to do an upgrade on a large XY table where the gantry is driven
by to oppositely mounted servo motors. Both sets of encoders run back to the
existing controller. Can I just give a generous deadband to the slave axis,
or is there a better way to address this configuration so the motors don't
fight each other. I believe it uses a single home switch which can then be
fed to both axes for purposes of homing. Anyone done this? Anything else to
look out for?

 

Thanks,

Eric

 

 
 
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