Re: [Emc-users] problem DH parameters manipulator arm

[Chris Albertson]

The problem to besolvedis that you need both forward and inverse kinematics.

Forward is where you have a set of joint angles and you want to know the
location and orientation of the end of the arm.This is easy for most
people who still remember trigonometry from high school.   If not go to Khan
Academy    And scroll down past
"first-grade math" to trig and linear algebra and differential equations
and sign up for whatever free classes you need.These are really good,
first tier level online classes.

Inverse is much harder.  THis is where you have the desired position and
orientation for the arm and yu want to knw the joint angles.   Many times
there are multiple solutions.Then, many times you want to maintain a
specified velocity or acceleration and you need to know the first and
second derivatives o the inverse kinematics.re-inventing this is really
hard unless you are using amachinewith triveal kinematics like most machine
tools.   But a 6 or 7 DOF arm is non-trivial.

That said, you have a textbook arm and you can find papers describing the
kinematics of palletizing robot arms were someone works out the math for
you.


That said, I still think the world to joint space conversion and motion
planning needs to be done in software that can "know" more about the world,
especially about obstacles such as pats and fixtures.  Arms can not move
through the parts you are trying to lift, so the planner needs to know
about the parts.   I'd to the joint-space control in something like MK and
the planning in something like Moveit.   Palletizing on not unlike "pick
and place"  in that not every object you lift is at some exact location so
moton must be planned in real-time.

On Sat, Mar 23, 2019 at 4:47 AM andy pugh  wrote:

> On Sat, 23 Mar 2019 at 00:45, yomin estiven jaramillo munera
>  wrote:
> >
> > Hi chris, i would like ask you something, based on you said , I need to
> > figure out how my elbow angle is moved in function to my base angle, and
> > after this i will need to add this function to my kinematics file, in
> that
> > case i would be using the DH parameters so, i should modificate
> genserkins,
> > shouldn't I?
>
> You don't have to use DH parameters or any matrix maths if you don't want
> to.
>
> You could just use everyday trigonometry, especially as your robot
> seems to work largely in a single plane.
>
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1916
>
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] problem DH parameters manipulator arm

[andy pugh]

On Sat, 23 Mar 2019 at 00:45, yomin estiven jaramillo munera
 wrote:
>
> Hi chris, i would like ask you something, based on you said , I need to
> figure out how my elbow angle is moved in function to my base angle, and
> after this i will need to add this function to my kinematics file, in that
> case i would be using the DH parameters so, i should modificate genserkins,
> shouldn't I?

You don't have to use DH parameters or any matrix maths if you don't want to.

You could just use everyday trigonometry, especially as your robot
seems to work largely in a single plane.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916


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Re: [Emc-users] problem DH parameters manipulator arm

[yomin estiven jaramillo munera]

Hi chris, i would like ask you something, based on you said , I need to
figure out how my elbow angle is moved in function to my base angle, and
after this i will need to add this function to my kinematics file, in that
case i would be using the DH parameters so, i should modificate genserkins,
shouldn't I?
do you have maybe some file which can help me about this function?

El jue., 21 de mar. de 2019 a la(s) 14:15, Chris Albertson (
albertson.ch...@gmail.com) escribió:

> I think what you have is a circular link.That means a
> parallelogram type geometry.  I have a robot arm like this too but mine
> is MUCH smaller and lower cost.
>
> Mine is nearly identical to this arm on Amazon.
> .amazon.com/Blesiya-Professional-Aluminum-Mechanical-Educational
> <
> https://www.amazon.com/Blesiya-Professional-Aluminum-Mechanical-Educational/dp/B07LCNBJJL/ref=sr_1_16?keywords=6dof+arm=1553194112=gateway=8-16
> >
>
> Notice that these are two motors on the shoulder and the "elbow" is pushed
> by a link.  I think we have the same geometries, except for scale.
> The way to model it using DH is to re-draw the robot arm.   Make a paper
> drawing of an equivalent arm that has a motor on each axis and no
> circular links and no passive links.You WILL need to transform the
> shaft angle of the moved motor.
>
> I don't use MK for this.  I like "move it" but still DH parameters really
> only work for serial links so the trick is to model your arm as a serial
> link arm, just pretend the elbow motor is on that elbow and it's shaft
> angle is a function of the base motor shaft angle.   This geometry is VERY
> common and yes there are names for it but most people call them palletizing
> robots.THese robots need to lift heavy loads, like bags of dog food off
> belts and place them on wood pallets so the motors are plased in the base
> and force transmitted to push rods.   Most are only 4-DOF   A Google search
> for "palletizing robot kinematics" will ,give tons of information.But
> "cheating" works.  Remove the pushlinks and move the motor and make DH
> parms for that.  The later "fix" the elbow motor shaft angle. .
>
> The arm in the above link is like mine in that it uses model airplane
> servos.   These are very inaccurate and are open loop.   So the plan is to
> close the control loop with a video cameras.  This is not something MK was
> designed for hence using Moveit. moveit.ros.orgThen I find I need to
> sychronize the video shutters so that is on hold for now.
>
>
> On Thu, Mar 21, 2019 at 6:45 AM yomin estiven jaramillo munera <
> yejm...@gmail.com> wrote:
>
> >  Hi guys is me again, our kinematics problem have progressed, this is
> > because we are sure that our D-H  parameters were correctly extracted,
> but
> > seems that our robot couldn't be defined with this parameters.
> > I'm saying this 'cause our robot is a miller MR 2000  and is very old, it
> > is moving how you can see in the follow link
> >
> > https://www.youtube.com/watch?v=Hp0gVXj5u-I=youtu.be
> >
> > the D-H parameters could define the kinematics but when a joint depend of
> > the before one, but in this case our joint 2 is not changing the
> > orientation of our joint 3. The joint 2 is able to change the position on
> > the space of the final tool, but is unable to change its orientation on
> the
> > space. this kinematics is obviously very different to PUMA kinematics and
> > we are doubting about DH parameters can solve this.
> > is there any name for this kind of kinematics?
> > could i solve this using D-H parameters?
> > could i solve this using genserkins?
> > All my axes are set like angular joint, could that involved in a possible
> > solution?
> >
> > 
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
> ___
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>

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Re: [Emc-users] problem DH parameters manipulator arm

[Chris Albertson]

I think what you have is a circular link.That means a
parallelogram type geometry.  I have a robot arm like this too but mine
is MUCH smaller and lower cost.

Mine is nearly identical to this arm on Amazon.
.amazon.com/Blesiya-Professional-Aluminum-Mechanical-Educational


Notice that these are two motors on the shoulder and the "elbow" is pushed
by a link.  I think we have the same geometries, except for scale.
The way to model it using DH is to re-draw the robot arm.   Make a paper
drawing of an equivalent arm that has a motor on each axis and no
circular links and no passive links.You WILL need to transform the
shaft angle of the moved motor.

I don't use MK for this.  I like "move it" but still DH parameters really
only work for serial links so the trick is to model your arm as a serial
link arm, just pretend the elbow motor is on that elbow and it's shaft
angle is a function of the base motor shaft angle.   This geometry is VERY
common and yes there are names for it but most people call them palletizing
robots.THese robots need to lift heavy loads, like bags of dog food off
belts and place them on wood pallets so the motors are plased in the base
and force transmitted to push rods.   Most are only 4-DOF   A Google search
for "palletizing robot kinematics" will ,give tons of information.But
"cheating" works.  Remove the pushlinks and move the motor and make DH
parms for that.  The later "fix" the elbow motor shaft angle. .

The arm in the above link is like mine in that it uses model airplane
servos.   These are very inaccurate and are open loop.   So the plan is to
close the control loop with a video cameras.  This is not something MK was
designed for hence using Moveit. moveit.ros.orgThen I find I need to
sychronize the video shutters so that is on hold for now.


On Thu, Mar 21, 2019 at 6:45 AM yomin estiven jaramillo munera <
yejm...@gmail.com> wrote:

>  Hi guys is me again, our kinematics problem have progressed, this is
> because we are sure that our D-H  parameters were correctly extracted, but
> seems that our robot couldn't be defined with this parameters.
> I'm saying this 'cause our robot is a miller MR 2000  and is very old, it
> is moving how you can see in the follow link
>
> https://www.youtube.com/watch?v=Hp0gVXj5u-I=youtu.be
>
> the D-H parameters could define the kinematics but when a joint depend of
> the before one, but in this case our joint 2 is not changing the
> orientation of our joint 3. The joint 2 is able to change the position on
> the space of the final tool, but is unable to change its orientation on the
> space. this kinematics is obviously very different to PUMA kinematics and
> we are doubting about DH parameters can solve this.
> is there any name for this kind of kinematics?
> could i solve this using D-H parameters?
> could i solve this using genserkins?
> All my axes are set like angular joint, could that involved in a possible
> solution?
>
> 
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] problem DH parameters manipulator arm

[andy pugh]

On Thu, 21 Mar 2019 at 15:34, yomin estiven jaramillo munera
 wrote:
>
> hi andy, how could trivkins take in count the size of my links?

You can't use trivkins, not at all.

I only showed the trivkins code to illustrate that a custom kinematics
module isn't very complicated. You just need to work out the
mathematical relationship between the joints and the coordinates of
the end-effector.
In trivkins this is very simple, with no calcualtions needed.
Your kinematics would need calculations specific to your geometry.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916


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Re: [Emc-users] problem DH parameters manipulator arm

[yomin estiven jaramillo munera]

hi andy, how could trivkins take in count the size of my links?

El jue., 21 de mar. de 2019 a la(s) 08:57, andy pugh (bodge...@gmail.com)
escribió:

> On Thu, 21 Mar 2019 at 13:45, yomin estiven jaramillo munera
>  wrote:
>
> > I'm saying this 'cause our robot is a miller MR 2000  and is very old, it
> > is moving how you can see in the follow link
>
> You are right, that isn't a "pure" serial robot so Genserkins is
> probably not a good choice.
>
> You could potentially add and subtract motor positions in HAL to make
> it work, but it is likely to be easier to write a custom kinematics
> from scratch.
>
> The robot seems to be geometrically fairly simple, being largely all
> in one plane.
>
> Look at the old version of trivkins to see how simple a kinematics file
> can be:
>
> https://github.com/LinuxCNC/linuxcnc/blob/2.6/src/emc/kinematics/trivkins.c
>
> Just two functions, one to calculate joint positions from world
> coordinates and one to do the reverse (everything after line 67 there
> is the same  in all kins files, unless they need pins, paramters etc)
>
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1916
>
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>

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Re: [Emc-users] problem DH parameters manipulator arm

[andy pugh]

On Thu, 21 Mar 2019 at 13:45, yomin estiven jaramillo munera
 wrote:

> I'm saying this 'cause our robot is a miller MR 2000  and is very old, it
> is moving how you can see in the follow link

You are right, that isn't a "pure" serial robot so Genserkins is
probably not a good choice.

You could potentially add and subtract motor positions in HAL to make
it work, but it is likely to be easier to write a custom kinematics
from scratch.

The robot seems to be geometrically fairly simple, being largely all
in one plane.

Look at the old version of trivkins to see how simple a kinematics file can be:

https://github.com/LinuxCNC/linuxcnc/blob/2.6/src/emc/kinematics/trivkins.c

Just two functions, one to calculate joint positions from world
coordinates and one to do the reverse (everything after line 67 there
is the same  in all kins files, unless they need pins, paramters etc)

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916


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[Emc-users] problem DH parameters manipulator arm

[yomin estiven jaramillo munera]

 Hi guys is me again, our kinematics problem have progressed, this is
because we are sure that our D-H  parameters were correctly extracted, but
seems that our robot couldn't be defined with this parameters.
I'm saying this 'cause our robot is a miller MR 2000  and is very old, it
is moving how you can see in the follow link

https://www.youtube.com/watch?v=Hp0gVXj5u-I=youtu.be

the D-H parameters could define the kinematics but when a joint depend of
the before one, but in this case our joint 2 is not changing the
orientation of our joint 3. The joint 2 is able to change the position on
the space of the final tool, but is unable to change its orientation on the
space. this kinematics is obviously very different to PUMA kinematics and
we are doubting about DH parameters can solve this.
is there any name for this kind of kinematics?
could i solve this using D-H parameters?
could i solve this using genserkins?
All my axes are set like angular joint, could that involved in a possible
solution?



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