Add geom adhesion: contacts that pull, via translated friction cones.
https://youtu.be/GioWwB36XHI The new geom attribute adhesion (units of force, signed; pair-level override) translates the contact friction cone along its normal so that the force origin lies strictly inside it. Consequences: each contact can pull with up to the given force before breaking, and the tangential friction budget becomes mu*(f_N + adhesion) -- the Mohr-Coulomb yield condition with cohesion c = mu*adhesion -- so lightly-squeezed grasps retain a guaranteed friction floor. A translated cone factors exactly into {constant attractive force} + {original cone}, so no solver kernels change. The implementation is this factorization: a constant attraction along contact normals accumulated into the new mjData.qfrc_adhesion (summed into qfrc_passive), plus a bias of adhesive contact rows' reference acceleration (aref += R*adhesion), which makes resting penetration exactly independent of adhesion. Contacts of adhesive pairs remain active throughout the gap zone, producing rows with positive violation whose reference acceleration pulls: a tether that resists pull-off smoothly, captures objects released within the band into steady contact, and detaches at the specified force. Adhesion values of the two geoms combine by sum; explicit pairs override. mj_contactForce reports the net interface force (cone force minus the adhesive pull), whose normal component can now be negative. Negative adhesion is allowed and produces a repulsive offset (air hockey). PiperOrigin-RevId: 950858148 Change-Id: I879c08eba7ae501e5c0f8c2f807167344da4c2bc
This commit is contained in:
Yuval Tassa
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Copybara-Service
Copybara-Service
parent
b942c9f922
commit
a264d0bc8b
@@ -1433,6 +1433,11 @@ STRUCTS: Mapping[str, StructDecl] = dict([
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type=ValueType(name='mjtBool'),
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doc='whether any geom has nonzero surfacevel',
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),
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StructFieldDecl(
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name='flg_adhesion',
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type=ValueType(name='mjtBool'),
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doc='whether any geom or pair has nonzero adhesion',
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),
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StructFieldDecl(
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name='opt',
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type=ValueType(name='mjOption'),
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@@ -2263,6 +2268,14 @@ STRUCTS: Mapping[str, StructDecl] = dict([
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doc='surface velocity in local frame: lin,ang',
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array_extent=('ngeom', 6),
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),
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StructFieldDecl(
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name='geom_adhesion',
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type=PointerType(
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inner_type=ValueType(name='mjtNum'),
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),
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doc='adhesive force of contacts',
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array_extent=('ngeom',),
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),
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StructFieldDecl(
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name='geom_fluid',
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type=PointerType(
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@@ -4031,6 +4044,14 @@ STRUCTS: Mapping[str, StructDecl] = dict([
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doc='additional contact detection buffer',
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array_extent=('npair',),
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),
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StructFieldDecl(
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name='pair_adhesion',
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type=PointerType(
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inner_type=ValueType(name='mjtNum'),
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),
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doc='adhesive force of contacts',
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array_extent=('npair',),
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),
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StructFieldDecl(
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name='pair_friction',
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type=PointerType(
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@@ -5409,6 +5430,11 @@ STRUCTS: Mapping[str, StructDecl] = dict([
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),
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doc='constraint solver impedance',
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),
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StructFieldDecl(
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name='adhesion',
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type=ValueType(name='mjtNum'),
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doc='adhesive force along the contact normal',
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),
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StructFieldDecl(
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name='mu',
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type=ValueType(name='mjtNum'),
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@@ -6415,6 +6441,14 @@ STRUCTS: Mapping[str, StructDecl] = dict([
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doc='passive fluid force',
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array_extent=('nv',),
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),
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StructFieldDecl(
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name='qfrc_adhesion',
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type=PointerType(
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inner_type=ValueType(name='mjtNum'),
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),
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doc='passive contact adhesion force',
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array_extent=('nv',),
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),
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StructFieldDecl(
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name='qfrc_passive',
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type=PointerType(
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@@ -7983,6 +8017,11 @@ STRUCTS: Mapping[str, StructDecl] = dict([
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),
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doc='surface velocity in local frame: linear, angular',
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),
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StructFieldDecl(
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name='adhesion',
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type=ValueType(name='double'),
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doc='adhesive force of contacts',
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),
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StructFieldDecl(
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name='mass',
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type=ValueType(name='double'),
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@@ -9256,6 +9295,11 @@ STRUCTS: Mapping[str, StructDecl] = dict([
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type=ValueType(name='double'),
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doc='additional contact detection buffer',
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),
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StructFieldDecl(
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name='adhesion',
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type=ValueType(name='double'),
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doc='adhesive force of contacts',
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),
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StructFieldDecl(
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name='friction',
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type=ArrayType(
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@@ -365,6 +365,13 @@ This is useful for example when the MJB is not available as a file on disk.)"));
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m.get()->flg_surfacevel = val;
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});
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mjModel.def_property(
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"flg_adhesion",
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[](const MjModelWrapper& m) { return m.get()->flg_adhesion; },
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[](MjModelWrapper& m, bool val) {
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m.get()->flg_adhesion = val;
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});
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#define X(var) \
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mjModel.def_property_readonly( \
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#var, [](const MjModelWrapper& m) { return m.get()->var; });
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@@ -770,6 +777,7 @@ This is useful for example when the MJB is not available as a file on disk.)"));
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})
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X(dist);
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X(includemargin);
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X(adhesion);
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X(mu);
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X(dim);
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X(geom1);
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@@ -821,6 +829,7 @@ This is useful for example when the MJB is not available as a file on disk.)"));
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XN(mjtNum, solref);
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XN(mjtNum, solreffriction);
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XN(mjtNum, solimp);
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X(mjtNum, adhesion);
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X(mjtNum, mu);
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XN(mjtNum, H);
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X(int, dim);
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