Hi

I am working on a stepping motor driver

To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988

https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988

For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA

In fast decay mode the rising and falling didt is thus 1A/ms

For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point�

If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%

So the magnetic field will cause quite a bit of torque ripple.�

Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?�

Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple

I don't see any mention of this, so it is probably insignificant...

Regards

Klaus�

--
Klaus

søndag den 26. december 2021 kl. 23.38.54 UTC+1 skrev Klaus Kragelund:
> Hi
>
>
> I am working on a stepping motor driver
>
>
> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>
> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>
>
> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>
>
> In fast decay mode the rising and falling didt is thus 1A/ms
>
>
> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>
>
> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>
>
> So the magnetic field will cause quite a bit of torque ripple.
>
>
> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>
> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>
> I don't see any mention of this, so it is probably insignificant...
>

isn't it such low current that a linear drive would work?

26.12.21 23:43, Lasse Langwadt Christensen wrote:
>s�ndag den 26. december 2021 kl. 23.38.54 UTC+1 skrev Klaus Kragelund:
>> Hi
>>
>>
>> I am working on a stepping motor driver
>>
>>
>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>>
>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>>
>>
>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>>
>>
>> In fast decay mode the rising and falling didt is thus 1A/ms
>>
>>
>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>>
>>
>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>>
>>
>> So the magnetic field will cause quite a bit of torque ripple.
>>
>>
>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>>
>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>>
>> I don't see any mention of this, so it is probably insignificant...
>>
>
>isn't it such low current that a linear drive would work?
>

The application is 20V/90mA, so 3.6W total. That will dissipate too much heat (industrial temperature specs)

But I like you idea of challenging how it is done ?

One could do an envelope converter fed to each half bridge (buck). But then it is very slow ramp up of the current

--
Klaus

26.12.21 23:55, Klaus Kragelund wrote:
>26.12.21 23:43, Lasse Langwadt Christensen wrote:
>>s?ndag den 26. december 2021 kl. 23.38.54 UTC+1 skrev Klaus Kragelund:
>>> Hi
>>>
>>>
>>> I am working on a stepping motor driver
>>>
>>>
>>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>>>
>>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>>>
>>>
>>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>>>
>>>
>>> In fast decay mode the rising and falling didt is thus 1A/ms
>>>
>>>
>>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>>>
>>>
>>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>>>
>>>
>>> So the magnetic field will cause quite a bit of torque ripple.
>>>
>>>
>>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>>>
>>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>>>
>>> I don't see any mention of this, so it is probably insignificant...
>>>
>>
>>isn't it such low current that a linear drive would work?
>>
>
>The application is 20V/90mA, so 3.6W total. That will dissipate too much heat (industrial temperature specs)
>
>But I like you idea of challenging how it is done ?
>
>One could do an envelope converter fed to each half bridge (buck). But then it is very slow ramp up of the current
>
>

Some ideas are centered around doing feed forward instead of current chopping. So like a VF control with a sinusoidal voltage vector so the current is without distortion around zero current. It will not be perfect, since it does then not regulate on the current

Perhaps a combination, with feed forward and current feedback to trim the wave shape

--
Klaus

søndag den 26. december 2021 kl. 23.55.09 UTC+1 skrev Klaus Kragelund:
> 26.12.21 23:43, Lasse Langwadt Christensen wrote:
> >søndag den 26. december 2021 kl. 23.38.54 UTC+1 skrev Klaus Kragelund:
> >> Hi
> >>
> >>
> >> I am working on a stepping motor driver
> >>
> >>
> >> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
> >>
> >> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
> >>
> >>
> >> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
> >>
> >>
> >> In fast decay mode the rising and falling didt is thus 1A/ms
> >>
> >>
> >> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
> >>
> >>
> >> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
> >>
> >>
> >> So the magnetic field will cause quite a bit of torque ripple.
> >>
> >>
> >> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
> >>
> >> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
> >>
> >> I don't see any mention of this, so it is probably insignificant...
> >>
> >
> >isn't it such low current that a linear drive would work?
> >
> The application is 20V/90mA, so 3.6W total. That will dissipate too much heat (industrial temperature specs)

only one coil will be fully on at a time, and at such high inductance the DC resistance must be quite high too
> But I like you idea of challenging how it is done ?
>
> One could do an envelope converter fed to each half bridge (buck). But then it is very slow ramp up of the current

it is basically a buck already, the inductor is just inside the motor

mandag den 27. december 2021 kl. 00.01.15 UTC+1 skrev Klaus Kragelund:
> 26.12.21 23:55, Klaus Kragelund wrote:
> >26.12.21 23:43, Lasse Langwadt Christensen wrote:
> >>s?ndag den 26. december 2021 kl. 23.38.54 UTC+1 skrev Klaus Kragelund:
> >>> Hi
> >>>
> >>>
> >>> I am working on a stepping motor driver
> >>>
> >>>
> >>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
> >>>
> >>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
> >>>
> >>>
> >>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
> >>>
> >>>
> >>> In fast decay mode the rising and falling didt is thus 1A/ms
> >>>
> >>>
> >>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
> >>>
> >>>
> >>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
> >>>
> >>>
> >>> So the magnetic field will cause quite a bit of torque ripple.
> >>>
> >>>
> >>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
> >>>
> >>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
> >>>
> >>> I don't see any mention of this, so it is probably insignificant...
> >>>
> >>
> >>isn't it such low current that a linear drive would work?
> >>
> >
> >The application is 20V/90mA, so 3.6W total. That will dissipate too much heat (industrial temperature specs)
> >
> >But I like you idea of challenging how it is done ?
> >
> >One could do an envelope converter fed to each half bridge (buck). But then it is very slow ramp up of the current
> >
> >
> Some ideas are centered around doing feed forward instead of current chopping. So like a VF control with a sinusoidal voltage vector so the current is without distortion around zero current. It will not be perfect, since it does then not regulate on the current
>
> Perhaps a combination, with feed forward and current feedback to trim the wave shape

afaict the Powerstep01 driver, in voltage mode, basically does pwm sinewaves with feedforward of speed, supply voltage, etc.

27.12.21 00:18, Lasse Langwadt Christensen wrote:
>s�ndag den 26. december 2021 kl. 23.55.09 UTC+1 skrev Klaus Kragelund:
>> 26.12.21 23:43, Lasse Langwadt Christensen wrote:
>> >s�ndag den 26. december 2021 kl. 23.38.54 UTC+1 skrev Klaus Kragelund:
>> >> Hi
>> >>
>> >>
>> >> I am working on a stepping motor driver
>> >>
>> >>
>> >> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>> >>
>> >> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>> >>
>> >>
>> >> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>> >>
>> >>
>> >> In fast decay mode the rising and falling didt is thus 1A/ms
>> >>
>> >>
>> >> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>> >>
>> >>
>> >> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>> >>
>> >>
>> >> So the magnetic field will cause quite a bit of torque ripple.
>> >>
>> >>
>> >> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>> >>
>> >> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>> >>
>> >> I don't see any mention of this, so it is probably insignificant...
>> >>
>> >
>> >isn't it such low current that a linear drive would work?
>> >
>> The application is 20V/90mA, so 3.6W total. That will dissipate too much heat (industrial temperature specs)
>
>only one coil will be fully on at a time, and at such high inductance the DC resistance must be quite high too
>
>> But I like you idea of challenging how it is done ?
>>
>> One could do an envelope converter fed to each half bridge (buck). But then it is very slow ramp up of the current
>
>it is basically a buck already, the inductor is just inside the motor
>
>
Yes. But for an envelope buck it can be filtered more, so torque ripple is reduced

--
Klaus

27.12.21 00:20, Lasse Langwadt Christensen wrote:
>mandag den 27. december 2021 kl. 00.01.15 UTC+1 skrev Klaus Kragelund:
>> 26.12.21 23:55, Klaus Kragelund wrote:
>> >26.12.21 23:43, Lasse Langwadt Christensen wrote:
>> >>s?ndag den 26. december 2021 kl. 23.38.54 UTC+1 skrev Klaus Kragelund:
>> >>> Hi
>> >>>
>> >>>
>> >>> I am working on a stepping motor driver
>> >>>
>> >>>
>> >>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>> >>>
>> >>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>> >>>
>> >>>
>> >>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>> >>>
>> >>>
>> >>> In fast decay mode the rising and falling didt is thus 1A/ms
>> >>>
>> >>>
>> >>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>> >>>
>> >>>
>> >>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>> >>>
>> >>>
>> >>> So the magnetic field will cause quite a bit of torque ripple.
>> >>>
>> >>>
>> >>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>> >>>
>> >>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>> >>>
>> >>> I don't see any mention of this, so it is probably insignificant...
>> >>>
>> >>
>> >>isn't it such low current that a linear drive would work?
>> >>
>> >
>> >The application is 20V/90mA, so 3.6W total. That will dissipate too much heat (industrial temperature specs)
>> >
>> >But I like you idea of challenging how it is done ?
>> >
>> >One could do an envelope converter fed to each half bridge (buck). But then it is very slow ramp up of the current
>> >
>> >
>> Some ideas are centered around doing feed forward instead of current chopping. So like a VF control with a sinusoidal voltage vector so the current is without distortion around zero current. It will not be perfect, since it does then not regulate on the current
>>
>> Perhaps a combination, with feed forward and current feedback to trim the wave shape
>
>afaict the Powerstep01 driver, in voltage mode, basically does pwm sinewaves with feedforward of speed, supply voltage, etc.
>
>
>
Sounds like I am reinvent the wheel ?

--
Klaus

On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>Hi
>
>
>I am working on a stepping motor driver
>
>
>To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>
>https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>
>
>For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>
>
>In fast decay mode the rising and falling didt is thus 1A/ms
>
>
>For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>
>
>If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>
>
>So the magnetic field will cause quite a bit of torque ripple.
>
>
>Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>
>Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>
>I don't see any mention of this, so it is probably insignificant...
>
>Regards
>
>
>Klaus

I did a microstepper once, for tuning superconductive microwave
cavities in an accelerator. It used a uP and a pair of integrated
h-bridge drivers.

It was basically a DDS synthesizer, a phase accumulator (representing
angular position) mapping into a sin-cos lookup table, which fetched
the duty cycle values to go into the pair of full h-bridges which
drove the motor coils. If the switching frequency is reasonably high,
there won't be noticable ripple torque.

My basically constant-voltage drive caused torque to drop off at high
step rates, which wasn't a problem in that application.

Most motors are imperfect in that you won't get smooth angular
position as a function of sin-cos coil currents; they basically have
distortion. That can be fudged in the trig lookup table if you really
need to.

--

I yam what I yam - Popeye

On 12/26/2021 3:38 PM, Klaus Kragelund wrote:
> I am working on a stepping motor driver

Is there a reason you are using a stepper motor and not another
type of motor? Usually, the stepper is chosen for precise (open-loop)
control of shaft rotational position -- usually requiring that position
to be held when the stepping stops. (as long as current remains
applied).

Microstepping shows poor performance, in this regard, when you
try to "hold" at anything other than a half/full step.

[Note that you can also drive a stepper as if a BLDC by monitoring
feedback from the other coils. But, this is prone to losing
sync if you miss a feedback event (the motor, usually operating at
accelerated speed, then drops a step and stalls)]

On 12/26/2021 5:08 PM, Don Y wrote:
> [Note that you can also drive a stepper as if a BLDC by monitoring
> feedback from the other coils. But, this is prone to losing
> sync if you miss a feedback event (the motor, usually operating at
> accelerated speed, then drops a step and stalls)]

<https://patents.google.com/patent/US4282471A/en>

On Monday, December 27, 2021 at 10:45:11 AM UTC+11, jla...@highlandsniptechnology.com wrote:
> On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
> <klau...@hotmail.com> wrote:

<snip>

> Most motors are imperfect in that you won't get smooth angular
> position as a function of sin-cos coil currents; they basically have
> distortion. That can be fudged in the trig lookup table if you really
> need to.

There was a paper in the (UK) Journal of Scientific Instruments in the 1970's that went into that in some detail - the correction table went into a PROM. If I remember rightly (and I probably don't) it was eight-bit accurate after correction, but the look-up table was ten bit words.

--
Bill Sloman, Sydney

mandag den 27. december 2021 kl. 00.26.26 UTC+1 skrev Klaus Kragelund:
> 27.12.21 00:20, Lasse Langwadt Christensen wrote:
> >mandag den 27. december 2021 kl. 00.01.15 UTC+1 skrev Klaus Kragelund:
> >> 26.12.21 23:55, Klaus Kragelund wrote:
> >> >26.12.21 23:43, Lasse Langwadt Christensen wrote:
> >> >>s?ndag den 26. december 2021 kl. 23.38.54 UTC+1 skrev Klaus Kragelund:
> >> >>> Hi
> >> >>>
> >> >>>
> >> >>> I am working on a stepping motor driver
> >> >>>
> >> >>>
> >> >>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
> >> >>>
> >> >>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
> >> >>>
> >> >>>
> >> >>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
> >> >>>
> >> >>>
> >> >>> In fast decay mode the rising and falling didt is thus 1A/ms
> >> >>>
> >> >>>
> >> >>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
> >> >>>
> >> >>>
> >> >>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
> >> >>>
> >> >>>
> >> >>> So the magnetic field will cause quite a bit of torque ripple.
> >> >>>
> >> >>>
> >> >>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
> >> >>>
> >> >>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
> >> >>>
> >> >>> I don't see any mention of this, so it is probably insignificant....
> >> >>>
> >> >>
> >> >>isn't it such low current that a linear drive would work?
> >> >>
> >> >
> >> >The application is 20V/90mA, so 3.6W total. That will dissipate too much heat (industrial temperature specs)
> >> >
> >> >But I like you idea of challenging how it is done ?
> >> >
> >> >One could do an envelope converter fed to each half bridge (buck). But then it is very slow ramp up of the current
> >> >
> >> >
> >> Some ideas are centered around doing feed forward instead of current chopping. So like a VF control with a sinusoidal voltage vector so the current is without distortion around zero current. It will not be perfect, since it does then not regulate on the current
> >>
> >> Perhaps a combination, with feed forward and current feedback to trim the wave shape
> >
> >afaict the Powerstep01 driver, in voltage mode, basically does pwm sinewaves with feedforward of speed, supply voltage, etc.
> >
> >
> >
> Sounds like I am reinvent the wheel ?

maybe :)

how cheap do you think you can make it? considering the low price of
stepdriver boards for 3D printers and the like the must be <$1 drivers
and that includes all the protection niceties

What is the DC resistance, rated voltage of the stepper motor and how
fast do you need to run it?

27.12.21 00:44, jlarkin@highlandsniptechnology.com wrote:
>On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
><klauskvik@hotmail.com> wrote:
>
>>Hi
>>
>>
>>I am working on a stepping motor driver
>>
>>
>>To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>>
>>https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>>
>>
>>For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>>
>>
>>In fast decay mode the rising and falling didt is thus 1A/ms
>>
>>
>>For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>>
>>
>>If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>>
>>
>>So the magnetic field will cause quite a bit of torque ripple.
>>
>>
>>Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>>
>>Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>>
>>I don't see any mention of this, so it is probably insignificant...
>>
>>Regards
>>
>>
>>Klaus
>
>I did a microstepper once, for tuning superconductive microwave
>cavities in an accelerator. It used a uP and a pair of integrated
>h-bridge drivers.
>
>It was basically a DDS synthesizer, a phase accumulator (representing
>angular position) mapping into a sin-cos lookup table, which fetched
>the duty cycle values to go into the pair of full h-bridges which
>drove the motor coils. If the switching frequency is reasonably high,
>there won't be noticable ripple torque.
>
>My basically constant-voltage drive caused torque to drop off at high
>step rates, which wasn't a problem in that application.
>
>Most motors are imperfect in that you won't get smooth angular
>position as a function of sin-cos coil currents; they basically have
>distortion. That can be fudged in the trig lookup table if you really
>need to.
>
>
>
That is the same as I was talking about with VF control. It the same used for Field Oriented Control of PMSM motors

--
Klaus

mandag den 27. december 2021 kl. 04.04.07 UTC+1 skrev bill....@ieee.org:
> On Monday, December 27, 2021 at 10:45:11 AM UTC+11, jla...@highlandsniptechnology.com wrote:
> > On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
> > <klau...@hotmail.com> wrote:
> <snip>
> > Most motors are imperfect in that you won't get smooth angular
> > position as a function of sin-cos coil currents; they basically have
> > distortion. That can be fudged in the trig lookup table if you really
> > need to.
> There was a paper in the (UK) Journal of Scientific Instruments in the 1970's that went into that in some detail - the correction table went into a PROM. If I remember rightly (and I probably don't) it was eight-bit accurate after correction, but the look-up table was ten bit words.
>

this one (section 19.2) https://www.trinamic.com/fileadmin/assets/Products/ICs_Documents/TMC2130_datasheet_Rev1.13.pdf
does a table for a quadrant with some trickery to make the table small

27.12.21 01:08, Don Y wrote:
>On 12/26/2021 3:38 PM, Klaus Kragelund wrote:
>> I am working on a stepping motor driver
>
>Is there a reason you are using a stepper motor and not another
>type of motor?

Yes. Client application need detent torque, and a stepper has lots of that

Also as I am told, to fit legacy products

>Usually, the stepper is chosen for precise (open-loop)
>control of shaft rotational position -- usually requiring that position
>to be held when the stepping stops. (as long as current remains
>applied).
>
>Microstepping shows poor performance, in this regard, when you
>try to "hold" at anything other than a half/full step.

Yes, micrstepping reduced the torque by at least 30%. And wastes energy to be sure of no missing steps
>
>[Note that you can also drive a stepper as if a BLDC by monitoring
>feedback from the other coils. But, this is prone to losing
>sync if you miss a feedback event (the motor, usually operating at
>accelerated speed, then drops a step and stalls)]

--
Klaus

On Mon, 27 Dec 2021 05:24:58 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>mandag den 27. december 2021 kl. 04.04.07 UTC+1 skrev bill....@ieee.org:
>> On Monday, December 27, 2021 at 10:45:11 AM UTC+11, jla...@highlandsniptechnology.com wrote:
>> > On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
>> > <klau...@hotmail.com> wrote:
>> <snip>
>> > Most motors are imperfect in that you won't get smooth angular
>> > position as a function of sin-cos coil currents; they basically have
>> > distortion. That can be fudged in the trig lookup table if you really
>> > need to.
>> There was a paper in the (UK) Journal of Scientific Instruments in the 1970's that went into that in some detail - the correction table went into a PROM. If I remember rightly (and I probably don't) it was eight-bit accurate after correction, but the look-up table was ten bit words.
>>
>
>this one (section 19.2) https://www.trinamic.com/fileadmin/assets/Products/ICs_Documents/TMC2130_datasheet_Rev1.13.pdf
>does a table for a quadrant with some trickery to make the table small
>
>

I had lots of memory available so I just folded the MSB to cut the
table size in half. More thinking can reduce it more. I guess one
could just compute sin and cos.

I also reduced the motor drives after a second of no motion.
Theoretically, the vector angle doesn't change if you reduce both
currents.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon

Klaus Kragelund <klauskvik@hotmail.com> wrote:

> Hi
>
>
> I am working on a stepping motor driver

If you want to try to do it in analogue:

http://www.poppyrecords.co.uk/ADM001/S05c/300MandrelMotorDriver.pdf

Circuit description on P31 of the manual:
http://www.poppyrecords.co.uk/ADM001/S05c/900Manual6d.pdf

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

On 12/27/2021 6:49 AM, Klaus Kragelund wrote:
> 27.12.21 01:08, Don Y wrote:
>> On 12/26/2021 3:38 PM, Klaus Kragelund wrote:
>>> I am working on a stepping motor driver
>>
>> Is there a reason you are using a stepper motor and not another
>> type of motor?
>
> Yes. Client application need detent torque, and a stepper has lots of that
>
> Also as I am told, to fit legacy products
>> Usually, the stepper is chosen for precise (open-loop)
>> control of shaft rotational position -- usually requiring that position
>> to be held when the stepping stops. (as long as current remains
>> applied).
>>
>> Microstepping shows poor performance, in this regard, when you
>> try to "hold" at anything other than a half/full step.
>
> Yes, micrstepping reduced the torque by at least 30%. And wastes energy to be
> sure of no missing steps

As long as you realize the holding torque varies considerably based on
whether you're on a full step, or not. We would always microstep for
smooth motion and good armature control... but always stop on full steps.

On Monday, December 27, 2021 at 10:45:11 AM UTC+11, jla...@highlandsniptechnology.com wrote:
> On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
> <klau...@hotmail.com> wrote:

<snip>
> Most motors are imperfect in that you won't get smooth angular position as a function of sin-cos coil currents; they basically have distortion. That can be fudged in the trig lookup table if you really need to.

If I remember rightly, Portescap claimed that some of their stepper motors gave much more uniform rotation than regular stepper motors.

Poking around their website didn't give me anything explicit but

https://www.portescap.com/en/products/miscellaneous/motion-innovations/outer-rotor-flat-brushless

seems to be claiming something like that.

https://www.portescap.com/en/products/stepper-motors/disc-magnet-motors

offer smaller than usual steps and "less detent torque" which might offer less distortion

--
Bill Sloman, Sydney

On 27/12/2021 00.44, jlarkin@highlandsniptechnology.com wrote:
> On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
> <klauskvik@hotmail.com> wrote:
>
>> Hi
>>
>>
>> I am working on a stepping motor driver
>>
>>
>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>>
>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>>
>>
>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>>
>>
>> In fast decay mode the rising and falling didt is thus 1A/ms
>>
>>
>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>>
>>
>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>>
>>
>> So the magnetic field will cause quite a bit of torque ripple.
>>
>>
>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>>
>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>>
>> I don't see any mention of this, so it is probably insignificant...
>>
>> Regards
>>
>>
>> Klaus
>
> I did a microstepper once, for tuning superconductive microwave
> cavities in an accelerator. It used a uP and a pair of integrated
> h-bridge drivers.
>
> It was basically a DDS synthesizer, a phase accumulator (representing
> angular position) mapping into a sin-cos lookup table, which fetched
> the duty cycle values to go into the pair of full h-bridges which
> drove the motor coils. If the switching frequency is reasonably high,
> there won't be noticable ripple torque.
>
> My basically constant-voltage drive caused torque to drop off at high
> step rates, which wasn't a problem in that application.
>
> Most motors are imperfect in that you won't get smooth angular
> position as a function of sin-cos coil currents; they basically have
> distortion. That can be fudged in the trig lookup table if you really
> need to.
>
So, now I am getting closer to having first prototype ready

I was doing the chopping control, peak current setting of the current in
the coils, a loop in the microcontroller that would control this peak
current with a DAC

Thinking about it, seems like it is all to no good. Just using the PWM
sine/cosine lookup table, with no feedback seems to work fine, provided
the speed of the motor is significantly below the max specified speed.
In that case BEMF has little effect, and really the winding resistance
sets the current according to applied voltage

Doing the open loop control would remove need for precise current
sensing and DACs (all though they could just be PWM outputs). Also
reduces the CPU resources needed for the control of the motor

I will keep the comparator to check for shorted halfbridge, at least for now

Cheers

Klaus

On Mon, 31 Jan 2022 01:52:20 +0100, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

>On 27/12/2021 00.44, jlarkin@highlandsniptechnology.com wrote:
>> On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
>> <klauskvik@hotmail.com> wrote:
>>
>>> Hi
>>>
>>>
>>> I am working on a stepping motor driver
>>>
>>>
>>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>>>
>>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>>>
>>>
>>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>>>
>>>
>>> In fast decay mode the rising and falling didt is thus 1A/ms
>>>
>>>
>>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>>>
>>>
>>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>>>
>>>
>>> So the magnetic field will cause quite a bit of torque ripple.
>>>
>>>
>>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>>>
>>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>>>
>>> I don't see any mention of this, so it is probably insignificant...
>>>
>>> Regards
>>>
>>>
>>> Klaus
>>
>> I did a microstepper once, for tuning superconductive microwave
>> cavities in an accelerator. It used a uP and a pair of integrated
>> h-bridge drivers.
>>
>> It was basically a DDS synthesizer, a phase accumulator (representing
>> angular position) mapping into a sin-cos lookup table, which fetched
>> the duty cycle values to go into the pair of full h-bridges which
>> drove the motor coils. If the switching frequency is reasonably high,
>> there won't be noticable ripple torque.
>>
>> My basically constant-voltage drive caused torque to drop off at high
>> step rates, which wasn't a problem in that application.
>>
>> Most motors are imperfect in that you won't get smooth angular
>> position as a function of sin-cos coil currents; they basically have
>> distortion. That can be fudged in the trig lookup table if you really
>> need to.
>>
>So, now I am getting closer to having first prototype ready
>
>I was doing the chopping control, peak current setting of the current in
>the coils, a loop in the microcontroller that would control this peak
>current with a DAC
>
>Thinking about it, seems like it is all to no good. Just using the PWM
>sine/cosine lookup table, with no feedback seems to work fine, provided
>the speed of the motor is significantly below the max specified speed.
>In that case BEMF has little effect, and really the winding resistance
>sets the current according to applied voltage
>
>Doing the open loop control would remove need for precise current
>sensing and DACs (all though they could just be PWM outputs). Also
>reduces the CPU resources needed for the control of the motor
>
>I will keep the comparator to check for shorted halfbridge, at least for now
>
>Cheers
>
>Klaus
>
>

Constant-voltage PWM will result in torque rolloff at high step rates,
and eventually stalling. More voltage with current feedback helps
stuff current into the winding inductance.

Some sort of pre-emphasis without feedback should work too.

--

I yam what I yam - Popeye

mandag den 31. januar 2022 kl. 02.33.22 UTC+1 skrev jla...@highlandsniptechnology.com:
> On Mon, 31 Jan 2022 01:52:20 +0100, Klaus Vestergaard Kragelund
> <klau...@hotmail.com> wrote:
>
> >On 27/12/2021 00.44, jla...@highlandsniptechnology.com wrote:
> >> On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
> >> <klau...@hotmail.com> wrote:
> >>
> >>> Hi
> >>>
> >>>
> >>> I am working on a stepping motor driver
> >>>
> >>>
> >>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
> >>>
> >>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
> >>>
> >>>
> >>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
> >>>
> >>>
> >>> In fast decay mode the rising and falling didt is thus 1A/ms
> >>>
> >>>
> >>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
> >>>
> >>>
> >>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
> >>>
> >>>
> >>> So the magnetic field will cause quite a bit of torque ripple.
> >>>
> >>>
> >>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
> >>>
> >>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
> >>>
> >>> I don't see any mention of this, so it is probably insignificant...
> >>>
> >>> Regards
> >>>
> >>>
> >>> Klaus
> >>
> >> I did a microstepper once, for tuning superconductive microwave
> >> cavities in an accelerator. It used a uP and a pair of integrated
> >> h-bridge drivers.
> >>
> >> It was basically a DDS synthesizer, a phase accumulator (representing
> >> angular position) mapping into a sin-cos lookup table, which fetched
> >> the duty cycle values to go into the pair of full h-bridges which
> >> drove the motor coils. If the switching frequency is reasonably high,
> >> there won't be noticable ripple torque.
> >>
> >> My basically constant-voltage drive caused torque to drop off at high
> >> step rates, which wasn't a problem in that application.
> >>
> >> Most motors are imperfect in that you won't get smooth angular
> >> position as a function of sin-cos coil currents; they basically have
> >> distortion. That can be fudged in the trig lookup table if you really
> >> need to.
> >>
> >So, now I am getting closer to having first prototype ready
> >
> >I was doing the chopping control, peak current setting of the current in
> >the coils, a loop in the microcontroller that would control this peak
> >current with a DAC
> >
> >Thinking about it, seems like it is all to no good. Just using the PWM
> >sine/cosine lookup table, with no feedback seems to work fine, provided
> >the speed of the motor is significantly below the max specified speed.
> >In that case BEMF has little effect, and really the winding resistance
> >sets the current according to applied voltage
> >
> >Doing the open loop control would remove need for precise current
> >sensing and DACs (all though they could just be PWM outputs). Also
> >reduces the CPU resources needed for the control of the motor
> >
> >I will keep the comparator to check for shorted halfbridge, at least for now
> >
> >Cheers
> >
> >Klaus
> >
> >
> Constant-voltage PWM will result in torque rolloff at high step rates,
> and eventually stalling. More voltage with current feedback helps
> stuff current into the winding inductance.
>
> Some sort of pre-emphasis without feedback should work too.

page 38, https://www.st.com/resource/en/datasheet/powerstep01.pdf

On 31/01/2022 02.33, jlarkin@highlandsniptechnology.com wrote:
> On Mon, 31 Jan 2022 01:52:20 +0100, Klaus Vestergaard Kragelund
> <klauskvik@hotmail.com> wrote:
>
>> On 27/12/2021 00.44, jlarkin@highlandsniptechnology.com wrote:
>>> On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
>>> <klauskvik@hotmail.com> wrote:
>>>
>>>> Hi
>>>>
>>>>
>>>> I am working on a stepping motor driver
>>>>
>>>>
>>>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>>>>
>>>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>>>>
>>>>
>>>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>>>>
>>>>
>>>> In fast decay mode the rising and falling didt is thus 1A/ms
>>>>
>>>>
>>>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>>>>
>>>>
>>>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>>>>
>>>>
>>>> So the magnetic field will cause quite a bit of torque ripple.
>>>>
>>>>
>>>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>>>>
>>>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>>>>
>>>> I don't see any mention of this, so it is probably insignificant...
>>>>
>>>> Regards
>>>>
>>>>
>>>> Klaus
>>>
>>> I did a microstepper once, for tuning superconductive microwave
>>> cavities in an accelerator. It used a uP and a pair of integrated
>>> h-bridge drivers.
>>>
>>> It was basically a DDS synthesizer, a phase accumulator (representing
>>> angular position) mapping into a sin-cos lookup table, which fetched
>>> the duty cycle values to go into the pair of full h-bridges which
>>> drove the motor coils. If the switching frequency is reasonably high,
>>> there won't be noticable ripple torque.
>>>
>>> My basically constant-voltage drive caused torque to drop off at high
>>> step rates, which wasn't a problem in that application.
>>>
>>> Most motors are imperfect in that you won't get smooth angular
>>> position as a function of sin-cos coil currents; they basically have
>>> distortion. That can be fudged in the trig lookup table if you really
>>> need to.
>>>
>> So, now I am getting closer to having first prototype ready
>>
>> I was doing the chopping control, peak current setting of the current in
>> the coils, a loop in the microcontroller that would control this peak
>> current with a DAC
>>
>> Thinking about it, seems like it is all to no good. Just using the PWM
>> sine/cosine lookup table, with no feedback seems to work fine, provided
>> the speed of the motor is significantly below the max specified speed.
>> In that case BEMF has little effect, and really the winding resistance
>> sets the current according to applied voltage
>>
>> Doing the open loop control would remove need for precise current
>> sensing and DACs (all though they could just be PWM outputs). Also
>> reduces the CPU resources needed for the control of the motor
>>
>> I will keep the comparator to check for shorted halfbridge, at least for now
>>
>> Cheers
>>
>> Klaus
>>
>>
>
> Constant-voltage PWM will result in torque rolloff at high step rates,
> and eventually stalling. More voltage with current feedback helps
> stuff current into the winding inductance.
>

Yes, that's why I wrote that my application has: "the speed of the motor
is significantly below the max specified speed"

> Some sort of pre-emphasis without feedback should work too.
>

In some cases the voltage PWM is better than current mode controlled.
For example, around the zero crossing where current feedback has distortion

On 31/01/2022 02.46, Lasse Langwadt Christensen wrote:
> mandag den 31. januar 2022 kl. 02.33.22 UTC+1 skrev jla...@highlandsniptechnology.com:
>> On Mon, 31 Jan 2022 01:52:20 +0100, Klaus Vestergaard Kragelund
>> <klau...@hotmail.com> wrote:
>>
>>> On 27/12/2021 00.44, jla...@highlandsniptechnology.com wrote:
>>>> On Sun, 26 Dec 2021 23:38:44 +0100, Klaus Kragelund
>>>> <klau...@hotmail.com> wrote:
>>>>
>>>>> Hi
>>>>>
>>>>>
>>>>> I am working on a stepping motor driver
>>>>>
>>>>>
>>>>> To reduce cost I will be making a discrete driver stage driven from a microcontroller that has all the control features that would normally be included in a micrstepping driver like the A4988
>>>>>
>>>>> https://www.allegromicro.com/en/products/motor-drivers/brush-dc-motor-drivers/a4988
>>>>>
>>>>>
>>>>> For easy calculation let's say the power stage is driven from 10V and the stepping motor has an inductance of 10mH and the peak current is 100mA
>>>>>
>>>>>
>>>>> In fast decay mode the rising and falling didt is thus 1A/ms
>>>>>
>>>>>
>>>>> For micro stepping the current in the 2 phases are set to place the armature in between a full step. So for a position 50% between two steps the currents in the windings are the same to have a resulting vector at that point
>>>>>
>>>>>
>>>>> If the on time is 5us, the ripple current is 5mApp. So, the current ripple is 5% of the nominal peak current. For lower excitation, at 10mA peak drive, the ripple is 50%
>>>>>
>>>>>
>>>>> So the magnetic field will cause quite a bit of torque ripple.
>>>>>
>>>>>
>>>>> Will this have any impact on the drive of the motor, or is the inertia so big that it is insignificant?
>>>>>
>>>>> Also, at other positions than 50%, the ripple with not cancel out between the phases and generate even more torque ripple
>>>>>
>>>>> I don't see any mention of this, so it is probably insignificant...
>>>>>
>>>>> Regards
>>>>>
>>>>>
>>>>> Klaus
>>>>
>>>> I did a microstepper once, for tuning superconductive microwave
>>>> cavities in an accelerator. It used a uP and a pair of integrated
>>>> h-bridge drivers.
>>>>
>>>> It was basically a DDS synthesizer, a phase accumulator (representing
>>>> angular position) mapping into a sin-cos lookup table, which fetched
>>>> the duty cycle values to go into the pair of full h-bridges which
>>>> drove the motor coils. If the switching frequency is reasonably high,
>>>> there won't be noticable ripple torque.
>>>>
>>>> My basically constant-voltage drive caused torque to drop off at high
>>>> step rates, which wasn't a problem in that application.
>>>>
>>>> Most motors are imperfect in that you won't get smooth angular
>>>> position as a function of sin-cos coil currents; they basically have
>>>> distortion. That can be fudged in the trig lookup table if you really
>>>> need to.
>>>>
>>> So, now I am getting closer to having first prototype ready
>>>
>>> I was doing the chopping control, peak current setting of the current in
>>> the coils, a loop in the microcontroller that would control this peak
>>> current with a DAC
>>>
>>> Thinking about it, seems like it is all to no good. Just using the PWM
>>> sine/cosine lookup table, with no feedback seems to work fine, provided
>>> the speed of the motor is significantly below the max specified speed.
>>> In that case BEMF has little effect, and really the winding resistance
>>> sets the current according to applied voltage
>>>
>>> Doing the open loop control would remove need for precise current
>>> sensing and DACs (all though they could just be PWM outputs). Also
>>> reduces the CPU resources needed for the control of the motor
>>>
>>> I will keep the comparator to check for shorted halfbridge, at least for now
>>>
>>> Cheers
>>>
>>> Klaus
>>>
>>>
>> Constant-voltage PWM will result in torque rolloff at high step rates,
>> and eventually stalling. More voltage with current feedback helps
>> stuff current into the winding inductance.
>>
>> Some sort of pre-emphasis without feedback should work too.
>
> page 38, https://www.st.com/resource/en/datasheet/powerstep01.pdf
>
Nice detailed datasheet, to learn from :-)