VRML Preparation for Robot Simulation/it: Difference between revisions
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== Esportare in VRML == |
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Export the document to a vrml file. The structure of the vrml file is the following: |
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Esportare il documento in un file VRML. |
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La struttura del file VRML è la seguente: |
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Revision as of 19:18, 12 May 2014
Questo tutorial spiega come utilizzare FreeCAD e l'ambiente Simulazione Robot per simulare i movimenti dei robot a 6 assi.
Il tutorial si concentra sulla creazione del file VRML utilizzato per la visualizzazione.
La base del file VRML è un modello di FreeCAD.
La versione di FreeCAD utilizzata è la 0.11.4252ppa1 in Ubuntu 32 bit.
Aprire un file o crearne uno con FreeCAD
Il tutorial si basa su un file STEP di un robot Stäubli TX40 (TX40-HB.stp).
È possibile scaricare il file file TX40-HB.stp da Stäubli.
Anche se non ho ancora avuto tempo di controllare, il metodo dovrebbe valere anche per un modello realizzato completamente in FreeCAD.
Dopo aver aperto il file, si dovrebbe ottenere questo:
Notare che, nell'importazione, il robot è composto di 8 forme, direttamente sulla radice dell'albero del documento.
La struttura del file VRML esportato può cambiare se sono utilizzati i gruppi. Le forme sono ordinate a partire dalla base allo strumento.
L'ultima forma contiene gli assi di rotazione di tutti gli assi del robot.
I nomi delle forme sono attribuiti in modo correlativo da FreeCAD, (dato che per ora (marzo 2011) FreeCAD non importa i nomi inclusi nei file STEP):
nome FreeCAD | nome STEP |
---|---|
TX40_HB | HORIZONTAL BASE CABLE OUTLET |
TX40_HB001 | SHOULDER |
TX40_HB002 | ARM |
TX40_HB003 | ELBOW |
TX40_HB004 | FOREARM |
TX40_HB005 | WRIST |
TX40_HB006 | TOOL FLANGE |
TX40_HB007 | ? |
In questa importazione, cambiare la modalità di visualizzazione, “Display Mode”, di ogni forma, ad eccezione di TX40_HB007, da "Flat Lines" a "Shaded" per dare un buon aspetto all'esportazione VRML. Ho anche cambiato i colori in [245, 196, 0] e [204, 204, 204] per farli corrispondere meglio al giallo di Stäubli.
Nascondere TX40_HB007 perché contiene gli assi di tutti i giunti e non può essere smontato.
Misure delle caratteristiche geometriche
Per costruire la tabella di Denavit-Hartenberg (vedere 6-Axis_Robot ) e per preparare il file VRML, è necessario ottenere le caratteristiche del Robot.
Per ora, lo strumento di misurazione di FreeCAD non è ancora pronto, è possibile utilizzare gli assi inclusi in TX40_HB007 (le coordinate sono indicate in basso a sinistra quando si punta un oggetto con il mouse), oppure si deve utilizzare la console Python per ottenere delle informazioni sulla geometria.
Notare che la Tabella DH è necessaria solo quando si ha bisogno di usare la cinematica inversa, ad esempio, per ottenere le coordinate cartesiane o guidare il robot con coordinate cartesiane.
La Tabella DH per questo robot è la seguente (mm, gradi e gradi/s) :
i | d | θ | r | α | θmin | θmax | Axis velocity |
---|---|---|---|---|---|---|---|
1 | 320 | q1 | 0 | -90 | -180 | 180 | 555 |
2 | 35 | q2 - 90 | 225 | 0 | -125 | 125 | 475 |
3 | 0 | q3 + 90 | 0 | 90 | -138 | 138 | 585 |
4 | 225 | q4 | 0 | -90 | -270 | 270 | 1035 |
5 | 0 | q5 | 0 | 90 | -120 | 133.5 | 1135 |
6 | 65 | q6 | 0 | 0 | -270 | 270 | 1575 |
Il file csv è quindi:
a , alpha, d , theta, rotDir, maxAngle, minAngle, AxisVelocity 0 , -90, 320, 0, 1, 180, -180, 555 225, 0, 35, -90, 1, 125, -125, 475 0 , 90, 0, 90, 1, 138, -138, 585 0 , -90, 225, 0, 1, 270, -270, 1035 0 , 90, 0, 0, 1, 133.5, -120, 1135 0 , 0, 65, 0, 1, 270, -270, 1575
Esportare in VRML
Esportare il documento in un file VRML. La struttura del file VRML è la seguente:
#VRML V2.0 utf8
Group {
children
Group {
children [
Group {
…
},
Group {
…
},
Group {
…
},
Group {
…
},
Group {
…
},
Group {
…
},
Group {
…
},
Group {
…
} ]
}
}
You can notice that we have 8 independent groups corresponding to the 8 shapes.
Preparation of the vrml file
All shapes in the vrml file are expressed in the base frame, independently from each other. For the Robot Simulation Workbench, we need to create a structure where a movement of a shape induces a movement of all shapes situated afterwards in the structure. The placement of the shapes will be relative to the preceding shape, so we need to include some translations from the absolute reference system to the relative one. The translations are described in the following picture:
With
- A=(0, 0, 168)
- B=(0, 107.8, 320)
- C=(0, 104.15, 545)
- D=(0, 35, 601)
- E=(0, 35, 770)
- F=(0, 35, 835).
Let's take the example of axis 4 between ELBOW and FOREARM, situated at D=(xd, yd, zd). The anchor for the FreeCAD axis is
"DEF FREECAD_AXIS4 Transform { rotation 0 1 0 0 children ["
This corresponds to a rotation about the y-axis. In the CAD model, the rotation is about the z-axis. Thus, we need to a rotation about the x-axis of before the FreeCAD axis definition and of after it. Also, a translation of (-xd, -yd, -zd) is needed just before the Group corresponding to the definition of FOREARM to express it in the relative reference frame centered at D. This means that a translation of (xd, yd, zd) must be inserted before the first rotation. At the end, the vrml-file from the definition of ELBOW to the definition of FOREARM looks like this:
# ELBOW
Group {
… here comes the unmodified definition of ELBOW
},
Transform {
translation 0 35 601
rotation 1 0 0 1.5707963
children
DEF FREECAD_AXIS4 Transform { rotation 0 1 0 0 children
Transform {
rotation 1 0 0 -1.5707963
children
Transform {
translation 0 -35 -601
children [
# FOREARM
Group {
... here comes the unmodified definition of FOREARM
},
At the end of the document, the appropriate closing brackets must be inserted: “ ]}}}},” for each of the 6 axes. Eventually, the document looks like this (I don't know if I can link the file here because of copyrights):
#VRML V2.0 utf8
Group {
children
Group {
children [
# HORIZONTAL BASE CABLE OUTLET
Group {
... here comes the unmodified definition of HORIZONTAL BASE CABLE OUTLET
},
Transform {
translation 0 0 168
rotation 1 0 0 1.5707963
children
DEF FREECAD_AXIS1 Transform { rotation 0 1 0 0 children
Transform {
rotation 1 0 0 -1.5707963
children
Transform {
translation 0 0 -168
children [
# SHOULDER
Group {
... here comes the unmodified definition of SHOULDER
},
Transform {
translation 0 107.8 320
#rotation 0 0 1 0
children
DEF FREECAD_AXIS2 Transform { rotation 0 1 0 0 children
Transform {
#rotation 0 0 1 0
children
Transform {
translation 0 -107.8 -320
children [
# ARM
Group {
... here comes the unmodified definition of ARM
},
Transform {
translation 0 104.15 545
#rotation 0 0 1 0
children
DEF FREECAD_AXIS3 Transform { rotation 0 1 0 0 children
Transform {
#rotation 0 0 1 0
children
Transform {
translation 0 -104.15 -545
children [
# ELBOW
Group {
... here comes the unmodified definition of ELBOW
},
Transform {
translation 0 35 601
rotation 1 0 0 1.5707963
children
DEF FREECAD_AXIS4 Transform { rotation 0 1 0 0 children
Transform {
rotation 1 0 0 -1.5707963
children
Transform {
translation 0 -35 -601
children [
# FOREARM
Group {
... here comes the unmodified definition of FOREARM
},
Transform {
translation 0 35 770
#rotation 0 0 1 0
children
DEF FREECAD_AXIS5 Transform { rotation 0 1 0 0 children
Transform {
#rotation 0 0 1 0
children
Transform {
translation 0 -35 -770
children [
# WRIST
Group {
... here comes the unmodified definition of WRIST
},
Transform {
translation 0 35 835
rotation 1 0 0 1.5707963
children
DEF FREECAD_AXIS6 Transform { rotation 0 1 0 0 children
Transform {
rotation 1 0 0 -1.5707963
children
Transform {
translation 0 -35 -835
children [
# TOOL FLANGE
Group {
... here comes the unmodified definition of TOOL FRAME
},
Group {
... here comes the unmodified definition of TX40_HB007
} # "]" was deleted from this line
]}}}},
]}}}},
]}}}},
]}}}},
]}}}},
]}}}},
] # this is the "]" deleted from the line above
}
}
Here is a patch to obtain the vrml file suitable for robot simulation:
7a8
> # HORIZONTAL BASE CABLE OUTLET
95968a95970,95981
> Transform {
> translation 0 0 168
> rotation 1 0 0 1.5707963
> children
> DEF FREECAD_AXIS1 Transform { rotation 0 1 0 0 children
> Transform {
> rotation 1 0 0 -1.5707963
> children
> Transform {
> translation 0 0 -168
> children [
> # SHOULDER
128428a128442,128453
> Transform {
> translation 0 107.8 320
> #rotation 0 0 1 0
> children
> DEF FREECAD_AXIS2 Transform { rotation 0 1 0 0 children
> Transform {
> #rotation 0 0 1 0
> children
> Transform {
> translation 0 -107.8 -320
> children [
> # ARM
206503a206529,206540
> Transform {
> translation 0 104.15 545
> #rotation 0 0 1 0
> children
> DEF FREECAD_AXIS3 Transform { rotation 0 1 0 0 children
> Transform {
> #rotation 0 0 1 0
> children
> Transform {
> translation 0 -104.15 -545
> children [
> # ELBOW
267111a267149,267160
> Transform {
> translation 0 35 601
> rotation 1 0 0 1.5707963
> children
> DEF FREECAD_AXIS4 Transform { rotation 0 1 0 0 children
> Transform {
> rotation 1 0 0 -1.5707963
> children
> Transform {
> translation 0 -35 -601
> children [
> # FOREARM
417854a417904,417915
> Transform {
> translation 0 35 770
> #rotation 0 0 1 0
> children
> DEF FREECAD_AXIS5 Transform { rotation 0 1 0 0 children
> Transform {
> #rotation 0 0 1 0
> children
> Transform {
> translation 0 -35 -770
> children [
> # WRIST
422053a422115,422126
> Transform {
> translation 0 35 835
> rotation 1 0 0 1.5707963
> children
> DEF FREECAD_AXIS6 Transform { rotation 0 1 0 0 children
> Transform {
> rotation 1 0 0 -1.5707963
> children
> Transform {
> translation 0 -35 -835
> children [
> # TOOL FLANGE
435627c435700,435707
< } ]
---
> }
> ]}}}},
> ]}}}},
> ]}}}},
> ]}}}},
> ]}}}},
> ]}}}},
> ]