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<mujoco model="Active adhesion example">
<!--
Adding some fluid viscosity to prevent the hanging sphere from jiggling too much.
-->
<option viscosity="1"/>
<size nconmax="500" njmax="1000"/>
<visual>
<headlight diffuse=".2 .2 .2"/>
</visual>
<default>
<joint damping=".3" axis="0 1 0"/>
<geom type="box" friction=".5"/>
<default class="wall">
<geom rgba=".5 .5 .5 .4"/>
</default>
<default class="mechanical">
<geom rgba=".5 .5 .8 1"/>
<tendon rgba=".5 .5 .8 1"/>
</default>
<default class="active_adhesion">
<!--
Geoms in the active_adhesion class are "inflated" with a margin of 1cm, but contacts are
activated only at a depth gap of 1cm, leading to a layer of inactive contacts at a 1cm
distance from the surface. However the contacts can be used by the adhesion actuator.
-->
<geom rgba=".8 .5 .5 1" margin=".01" gap=".01"/>
</default>
<default class="object">
<geom rgba=".5 .8 .5 1" density="100"/>
</default>
</default>
<worldbody>
<light pos="0.4 -.15 .6" dir="-1 .5 -1" diffuse=".7 .7 .7"/>
<light pos="-.4 -.15 .6" dir="1 .5 -1" diffuse=".7 .7 .7"/>
<body name="two crates">
<joint name="conveyor" type="slide" damping="100" axis="1 0 0"/>
<geom size=".2 .1 .01" pos="0 0 -.01"/>
<geom size=".01 .08 .031" pos="-.19 0 .03" class="wall"/>
<geom size=".01 .08 .031" pos="0 0 .03" class="wall"/>
<geom size=".01 .08 .031" pos="0.19 0 .03" class="wall"/>
<geom size="0.2 .01 .031" pos="0 -.09 .03" class="wall"/>
<geom size="0.2 .01 .031" pos="0 0.09 .03" class="wall"/>
</body>
<body name="arm1" pos="-.1 0 .3" childclass="mechanical">
<joint name="arm1"/>
<geom type="cylinder" size=".015 .01" zaxis="0 1 0"/>
<geom type="capsule" size=".01" fromto="0 0 0 -.12 0 -.07"/>
<body name="arm2" pos="-.12 0 -.07">
<joint name="arm2"/>
<geom type="cylinder" size=".015 .01" zaxis="0 1 0"/>
<geom type="capsule" size=".01" fromto="0 0 0 .12 0 -.07"/>
<body name="4boxes" pos=".12 0 -.08" childclass="active_adhesion">
<site name="force_sensor" group="3"/>
<joint name="arm3" damping=".01" pos="0 -.03 0"/>
<geom size=".015 .015 .01" pos="0.015 0.015 0"/>
<geom size=".015 .015 .01" pos="0.015 -.015 0"/>
<geom size=".015 .015 .01" pos="-.015 0.015 0"/>
<geom size=".015 .015 .01" pos="-.015 -.015 0"/>
</body>
</body>
</body>
<body name="box" pos="-.1 0 .05">
<freejoint/>
<geom size=".05 .05 .05" class="object"/>
</body>
<body name="winch" pos="-.01 0 .35" childclass="mechanical">
<joint name="winch" damping="1"/>
<geom type="cylinder" size=".015 .01" zaxis="0 1 0"/>
<geom type="capsule" size=".01" fromto="0 0 0 .1 0 .05"/>
<site name="anchor" pos=".1 0 .04"/>
</body>
<site name="pulley" pos=".1 0 .32"/>
<site name="hook_left" pos=".08 0 .3"/>
<site name="hook_right" pos=".12 0 .3"/>
<body name="sphere" pos=".1 0 .2" childclass="active_adhesion">
<freejoint/>
<!--
The composite balls in the crate have only 3 linear DoFs with condim=1, effectively
frictionless point particles. In order to make them stick to the sphere we give the sphere
priority 2, to force condim=3.
Also note the sphere has a margin+gap of 3cm as opposed to the 1cm of the arm box.
-->
<geom type="sphere" size=".03" priority="2" margin=".03" gap=".03"/>
<site name="pin_left" pos="-.025 0 .025"/>
<site name="pin_right" pos=".025 0 .025"/>
</body>
<composite type="particle" count="4 4 4" spacing="0.025" offset=".11 .01 .1">
<geom size=".012" rgba=".5 .8 .5 1" solref=".005 1"/>
</composite>
</worldbody>
<equality>
<joint joint1="arm1" joint2="arm2" polycoef="0 -.5 0 0 0"/>
<joint joint1="arm3" joint2="arm1"/>
</equality>
<!--
By using divisor=3 in the pullies we increase the distance by which the hanging sphere moves
relative to the motion of the winch arm. One should imagine a double spindle with two radii that
creates a ratio of 1.5 between the motion of tendon before the pullies and after the pullies.
(1.5 rather than 3 because the tendon has 2 branches and the length is split between them)
-->
<tendon>
<spatial range="0 .19" limited="true" solreflimit=".01 2" class="mechanical">
<site site="anchor"/>
<site site="pulley"/>
<pulley divisor="3"/>
<site site="pulley"/>
<site site="hook_left"/>
<site site="pin_left"/>
<pulley divisor="3"/>
<site site="pulley"/>
<site site="hook_right"/>
<site site="pin_right"/>
</spatial>
</tendon>
<actuator>
<position name="conveyor" joint="conveyor" ctrlrange="-.2 .2" ctrllimited="true" kp="400"/>
<position name="arm" joint="arm2" ctrlrange="-.8 1" ctrllimited="true" kp="10"/>
<adhesion name="adhere_arm" body="4boxes" ctrlrange="0 1" gain="5"/>
<position name="winch" joint="winch" ctrlrange="-.7 .5" ctrllimited="true" kp="10"/>
<adhesion name="adhere_winch" body="sphere" ctrlrange="0 1" gain="5"/>
</actuator>
<sensor>
<force site="force_sensor"/>
</sensor>
</mujoco>
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