How to use DH parameter extractor.ttm?

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w1574587
Posts: 9
Joined: 25 Oct 2020, 03:42

How to use DH parameter extractor.ttm?

Post by w1574587 »

I'm using DH parameter extractor.ttm to extract the DH parameter of Sawyer.ttm. The joint angles are all set to be 0. However, when clicking the joint 1 and joint 2, the popped console gives me different results:

Code: Select all


Between 'Sawyer_joint1' and 'Sawyer_headJoint':
    d=0.0000
    theta=0.0
    a=0.0000
    alpha=0.0

Between 'Sawyer_joint1' and 'Sawyer_joint2':
    d=0.2305
    theta=-12.7
    a=0.0830
    alpha=-90.0

Between 'Sawyer_joint2' and 'Sawyer_joint3':
    d=0.1829
    theta=180.0
    a=0.1470
    alpha=77.3

Between 'Sawyer_joint3' and 'Sawyer_joint4':
    d=0.0276
    theta=166.0
    a=0.5026
    alpha=77.6

Between 'Sawyer_joint4' and 'Sawyer_joint5':
    d=-0.1829
    theta=3.7
    a=0.0159
    alpha=90.9

Between 'Sawyer_joint5' and 'Sawyer_joint6':
    d=0.0046
    theta=-0.9
    a=0.3811
    alpha=-90.9

Between 'Sawyer_joint6' and 'Sawyer_joint7':
    d=0.1359
    theta=179.3
    a=0.0113
    alpha=90.1

Between 'Sawyer_joint7' and 'BaxterGripper_centerJoint':
    d=0.0001
    theta=-179.9
    a=0.2629
    alpha=-89.9

Between 'BaxterGripper_centerJoint' and 'BaxterGripper_closeJoint':
    d=0.0000
    theta=0.0
    a=0.0000
    alpha=0.0

Code: Select all

Between 'Sawyer_joint2' and 'Sawyer_joint3':
    d=0.1315
    theta=89.8
    a=0.0189
    alpha=90.0

Between 'Sawyer_joint3' and 'Sawyer_joint4':
    d=0.0011
    theta=180.0
    a=0.4188
    alpha=90.0

Between 'Sawyer_joint4' and 'Sawyer_joint5':
    d=-0.1685
    theta=0.3
    a=0.0163
    alpha=90.0

Between 'Sawyer_joint5' and 'Sawyer_joint6':
    d=0.0008
    theta=-0.0
    a=0.3837
    alpha=-90.0

Between 'Sawyer_joint6' and 'Sawyer_joint7':
    d=0.1363
    theta=179.9
    a=0.0117
    alpha=90.0

Between 'Sawyer_joint7' and 'BaxterGripper_centerJoint':
    d=0.0000
    theta=180.0
    a=0.2631
    alpha=-90.0

Between 'BaxterGripper_centerJoint' and 'BaxterGripper_closeJoint':
    d=0.0000
    theta=0.0
    a=0.0000
    alpha=0.0

which makes me confused. (1) Why the parameters of 'Sawyer_joint2' and 'Sawyer_joint3' (and some of others) change? (2) Where are the zero joint angles I set in advance? Is the 'theta' in the console actually the 'offset' of DH parameter?
And if you are willing to, (3) could you please provide me the right DH parameter of Sawyer.ttm?

Cheers

coppelia
Site Admin
Posts: 10336
Joined: 14 Dec 2012, 00:25

Re: How to use DH parameter extractor.ttm?

Post by coppelia »

Hello,

yes, it appears that the tool is broken... we'll look into this

Cheers

Raines-only
Posts: 1
Joined: 09 Dec 2021, 17:11

Re: How to use DH parameter extractor.ttm?

Post by Raines-only »

Hello,
I'm using version 4.1. Is the dh parameter extracted from the toolbox standard or modified, and the DH parameter measurement results are related to joints?
Thanks!

coppelia
Site Admin
Posts: 10336
Joined: 14 Dec 2012, 00:25

Re: How to use DH parameter extractor.ttm?

Post by coppelia »

I think in that version the tool is also broken. You should try to extract the DH parameters from the relative transformation matrix between successive joints. e.g.

Code: Select all

local m=sim.getObjectMatrix(joint2,joint1)
-- m contains 12 values (last 4 values are omitted):
m1  m2  m3  m4
m5  m6  m7  m8
m9  m10 m11 m12
0   0   0   1

-- Left 3X3 part is the rotation matrix, [m4, m8, 12] is the position of the frame.
Cheers

SevenTRI
Posts: 15
Joined: 19 Mar 2022, 10:32

Re: How to use DH parameter extractor.ttm?

Post by SevenTRI »

coppelia wrote: 09 Mar 2021, 08:03 Hello,

yes, it appears that the tool is broken... we'll look into this

Cheers
For version 4.3, this problem still exists, is it still not solved?

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