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Add geom adhesion: contacts that pull, via translated friction cones.

Browse Source 
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
2026-07-20 08:35:17 -07:00
committed by Copybara-Service
parent b942c9f922
commit a264d0bc8b
28 changed files with 784 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files
wasm/codegen/generated/bindings.cc
+7
View File
@@ -4502,6 +4502,7 @@ EMSCRIPTEN_BINDINGS(mujoco_bindings) {
.constructor<>()
.function("copy", &MjContact::copy, take_ownership())
.property("H", &MjContact::H)
.property("adhesion", &MjContact::adhesion, &MjContact::set_adhesion, reference())
.property("dim", &MjContact::dim, &MjContact::set_dim, reference())
.property("dist", &MjContact::dist, &MjContact::set_dist, reference())
.property("efc_address", &MjContact::efc_address, &MjContact::set_efc_address, reference())
@@ -4685,6 +4686,7 @@ EMSCRIPTEN_BINDINGS(mujoco_bindings) {
.property("qacc_smooth", &MjData::qacc_smooth)
.property("qacc_warmstart", &MjData::qacc_warmstart)
.property("qfrc_actuator", &MjData::qfrc_actuator)
.property("qfrc_adhesion", &MjData::qfrc_adhesion)
.property("qfrc_applied", &MjData::qfrc_applied)
.property("qfrc_bias", &MjData::qfrc_bias)
.property("qfrc_constraint", &MjData::qfrc_constraint)
@@ -4982,9 +4984,11 @@ EMSCRIPTEN_BINDINGS(mujoco_bindings) {
.property("flexvert_J_colind", &MjModel::flexvert_J_colind)
.property("flexvert_J_rowadr", &MjModel::flexvert_J_rowadr)
.property("flexvert_J_rownnz", &MjModel::flexvert_J_rownnz)
.property("flg_adhesion", &MjModel::flg_adhesion, &MjModel::set_flg_adhesion, reference())
.property("flg_gravcomp", &MjModel::flg_gravcomp, &MjModel::set_flg_gravcomp, reference())
.property("flg_surfacevel", &MjModel::flg_surfacevel, &MjModel::set_flg_surfacevel, reference())
.property("geom_aabb", &MjModel::geom_aabb)
.property("geom_adhesion", &MjModel::geom_adhesion)
.property("geom_bodyid", &MjModel::geom_bodyid)
.property("geom_conaffinity", &MjModel::geom_conaffinity)
.property("geom_condim", &MjModel::geom_condim)
@@ -5240,6 +5244,7 @@ EMSCRIPTEN_BINDINGS(mujoco_bindings) {
.property("oct_coeff", &MjModel::oct_coeff)
.property("oct_depth", &MjModel::oct_depth)
.property("opt", &MjModel::opt, reference())
.property("pair_adhesion", &MjModel::pair_adhesion)
.property("pair_dim", &MjModel::pair_dim)
.property("pair_friction", &MjModel::pair_friction)
.property("pair_gap", &MjModel::pair_gap)
@@ -5752,6 +5757,7 @@ EMSCRIPTEN_BINDINGS(mujoco_bindings) {
.property("pos", &MjsFrame::pos)
.property("quat", &MjsFrame::quat);
emscripten::class_<MjsGeom>("MjsGeom")
.property("adhesion", &MjsGeom::adhesion, &MjsGeom::set_adhesion, reference())
.property("alt", &MjsGeom::alt, reference())
.property("conaffinity", &MjsGeom::conaffinity, &MjsGeom::set_conaffinity, reference())
.property("condim", &MjsGeom::condim, &MjsGeom::set_condim, reference())
@@ -5895,6 +5901,7 @@ EMSCRIPTEN_BINDINGS(mujoco_bindings) {
.property("xyaxes", &MjsOrientation::xyaxes)
.property("zaxis", &MjsOrientation::zaxis);
emscripten::class_<MjsPair>("MjsPair")
.property("adhesion", &MjsPair::adhesion, &MjsPair::set_adhesion, reference())
.property("condim", &MjsPair::condim, &MjsPair::set_condim, reference())
.property("element", &MjsPair::element, reference())
.property("friction", &MjsPair::friction)
wasm/codegen/generated/bindings.h
+33
View File
@@ -377,6 +377,12 @@ struct MjContact {
emscripten::val solimp() const {
return emscripten::val(emscripten::typed_memory_view(5, ptr_->solimp));
}
mjtNum adhesion() const {
return ptr_->adhesion;
}
void set_adhesion(mjtNum value) {
ptr_->adhesion = value;
}
mjtNum mu() const {
return ptr_->mu;
}
@@ -3091,6 +3097,12 @@ struct MjsPair {
void set_gap(double value) {
ptr_->gap = value;
}
double adhesion() const {
return ptr_->adhesion;
}
void set_adhesion(double value) {
ptr_->adhesion = value;
}
emscripten::val friction() const {
return emscripten::val(emscripten::typed_memory_view(5, ptr_->friction));
}
@@ -4320,6 +4332,12 @@ struct MjModel {
void set_flg_surfacevel(mjtBool value) {
ptr_->flg_surfacevel = value;
}
mjtBool flg_adhesion() const {
return ptr_->flg_adhesion;
}
void set_flg_adhesion(mjtBool value) {
ptr_->flg_adhesion = value;
}
emscripten::val buffer() const {
return emscripten::val(emscripten::typed_memory_view(ptr_->nbuffer, static_cast<uint8_t*>(ptr_->buffer)));
}
@@ -4626,6 +4644,9 @@ struct MjModel {
emscripten::val geom_surfacevel() const {
return emscripten::val(emscripten::typed_memory_view(ptr_->ngeom * 6, ptr_->geom_surfacevel));
}
emscripten::val geom_adhesion() const {
return emscripten::val(emscripten::typed_memory_view(ptr_->ngeom, ptr_->geom_adhesion));
}
emscripten::val geom_fluid() const {
return emscripten::val(emscripten::typed_memory_view(ptr_->ngeom * mjNFLUID, ptr_->geom_fluid));
}
@@ -5289,6 +5310,9 @@ struct MjModel {
emscripten::val pair_gap() const {
return emscripten::val(emscripten::typed_memory_view(ptr_->npair, ptr_->pair_gap));
}
emscripten::val pair_adhesion() const {
return emscripten::val(emscripten::typed_memory_view(ptr_->npair, ptr_->pair_adhesion));
}
emscripten::val pair_friction() const {
return emscripten::val(emscripten::typed_memory_view(ptr_->npair * 5, ptr_->pair_friction));
}
@@ -6290,6 +6314,12 @@ struct MjsGeom {
emscripten::val surfacevel() const {
return emscripten::val(emscripten::typed_memory_view(6, ptr_->surfacevel));
}
double adhesion() const {
return ptr_->adhesion;
}
void set_adhesion(double value) {
ptr_->adhesion = value;
}
double mass() const {
return ptr_->mass;
}
@@ -7055,6 +7085,9 @@ struct MjData {
emscripten::val qfrc_fluid() const {
return emscripten::val(emscripten::typed_memory_view(model->nv, ptr_->qfrc_fluid));
}
emscripten::val qfrc_adhesion() const {
return emscripten::val(emscripten::typed_memory_view(model->nv, ptr_->qfrc_adhesion));
}
emscripten::val qfrc_passive() const {
return emscripten::val(emscripten::typed_memory_view(model->nv, ptr_->qfrc_passive));
}