Contact Sensor#
The contact sensor is designed to return the net contact force acting on a given ridgid body. The sensor is written to behave as a physical object, and so the “scope” of the contact sensor is limited to the body (or bodies) that defines it. There are multiple ways to define this scope, depending on your need to filter the forces coming from the contact.
By default, the reported force is the total contact force, but your application may only care about contact forces due to specific objects. Retrieving contact forces from specific objects requires filtering, and this can only be done in a “many-to-one” way. A multi-legged robot that needs filterable contact information for its feet would require one sensor per foot to be defined in the environment, but a robotic hand with contact sensors on the tips of each finger can be defined with a single sensor.
Consider a simple environment with an Anymal Quadruped and a block
@configclass
class ContactSensorSceneCfg(InteractiveSceneCfg):
"""Design the scene with sensors on the robot."""
# ground plane
ground = AssetBaseCfg(prim_path="/World/defaultGroundPlane", spawn=sim_utils.GroundPlaneCfg())
# lights
dome_light = AssetBaseCfg(
prim_path="/World/Light", spawn=sim_utils.DomeLightCfg(intensity=3000.0, color=(0.75, 0.75, 0.75))
)
# robot
robot = ANYMAL_C_CFG.replace(prim_path="{ENV_REGEX_NS}/Robot")
# Rigid Object
cube = RigidObjectCfg(
prim_path="{ENV_REGEX_NS}/Cube",
spawn=sim_utils.CuboidCfg(
size=(0.5, 0.5, 0.1),
rigid_props=sim_utils.RigidBodyPropertiesCfg(),
mass_props=sim_utils.MassPropertiesCfg(mass=100.0),
collision_props=sim_utils.CollisionPropertiesCfg(),
physics_material=sim_utils.RigidBodyMaterialCfg(static_friction=1.0),
visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.0, 1.0, 0.0), metallic=0.2),
),
init_state=RigidObjectCfg.InitialStateCfg(pos=(0.5, 0.5, 0.05)),
)
contact_forces_LF = ContactSensorCfg(
prim_path="{ENV_REGEX_NS}/Robot/LF_FOOT",
update_period=0.0,
history_length=6,
debug_vis=True,
filter_prim_paths_expr=["{ENV_REGEX_NS}/Cube"],
)
contact_forces_RF = ContactSensorCfg(
prim_path="{ENV_REGEX_NS}/Robot/RF_FOOT",
update_period=0.0,
history_length=6,
debug_vis=True,
filter_prim_paths_expr=["{ENV_REGEX_NS}/Cube"],
)
contact_forces_H = ContactSensorCfg(
prim_path="{ENV_REGEX_NS}/Robot/.*H_FOOT",
update_period=0.0,
history_length=6,
We define the sensors on the feet of the robot in two different ways. The front feet are independent sensors (one sensor body per foot) and the “Cube” is placed under the left foot. The hind feet are defined as a single sensor with multiple bodies.
We can then run the scene and print the data from the sensors
def run_simulator(sim: sim_utils.SimulationContext, scene: InteractiveScene):
.
.
.
# Simulate physics
while simulation_app.is_running():
.
.
.
# print information from the sensors
print("-------------------------------")
print(scene["contact_forces_LF"])
print("Received force matrix of: ", scene["contact_forces_LF"].data.force_matrix_w)
print("Received contact force of: ", scene["contact_forces_LF"].data.net_forces_w)
print("-------------------------------")
print(scene["contact_forces_RF"])
print("Received force matrix of: ", scene["contact_forces_RF"].data.force_matrix_w)
print("Received contact force of: ", scene["contact_forces_RF"].data.net_forces_w)
print("-------------------------------")
print(scene["contact_forces_H"])
print("Received force matrix of: ", scene["contact_forces_H"].data.force_matrix_w)
print("Received contact force of: ", scene["contact_forces_H"].data.net_forces_w)
Here, we print both the net contact force and the filtered force matrix for each contact sensor defined in the scene. The front left and front right feet report the following
-------------------------------
Contact sensor @ '/World/envs/env_.*/Robot/LF_FOOT':
view type : <class 'omni.physics.tensors.api.RigidBodyView'>
update period (s) : 0.0
number of bodies : 1
body names : ['LF_FOOT']
Received force matrix of: tensor([[[[-1.3923e-05, 1.5727e-04, 1.1032e+02]]]], device='cuda:0')
Received contact force of: tensor([[[-1.3923e-05, 1.5727e-04, 1.1032e+02]]], device='cuda:0')
-------------------------------
Contact sensor @ '/World/envs/env_.*/Robot/RF_FOOT':
view type : <class 'omni.physics.tensors.api.RigidBodyView'>
update period (s) : 0.0
number of bodies : 1
body names : ['RF_FOOT']
Received force matrix of: tensor([[[[0., 0., 0.]]]], device='cuda:0')
Received contact force of: tensor([[[1.3529e-05, 0.0000e+00, 1.0069e+02]]], device='cuda:0')
Notice that even with filtering, both sensors report the net contact force acting on the foot. However, the “force matrix” on the right foot is zero because that foot isn’t in contact with the filtered body, /World/envs/env_.*/Cube. Now, checkout the data coming from the hind feet!
-------------------------------
Contact sensor @ '/World/envs/env_.*/Robot/.*H_FOOT':
view type : <class 'omni.physics.tensors.api.RigidBodyView'>
update period (s) : 0.0
number of bodies : 2
body names : ['LH_FOOT', 'RH_FOOT']
Received force matrix of: None
Received contact force of: tensor([[[9.7227e-06, 0.0000e+00, 7.2364e+01],
[2.4322e-05, 0.0000e+00, 1.8102e+02]]], device='cuda:0')
In this case, the contact sensor has two bodies: the left and right hind feet. When the force matrix is queried, the result is None because this is a many body sensor, and presently Isaac Lab only supports “many to one” contact force filtering. Unlike the single body contact sensor, the reported force tensor has multiple entries, with each “row” corresponding to the contact force on a single body of the sensor (matching the ordering at construction).
Code for contact_sensor.py
1# Copyright (c) 2022-2026, The Isaac Lab Project Developers (https://github.com/isaac-sim/IsaacLab/blob/main/CONTRIBUTORS.md).
2# All rights reserved.
3#
4# SPDX-License-Identifier: BSD-3-Clause
5
6"""Launch Isaac Sim Simulator first."""
7
8import argparse
9
10from isaaclab.app import AppLauncher
11
12# add argparse arguments
13parser = argparse.ArgumentParser(description="Example on using the contact sensor.")
14parser.add_argument("--num_envs", type=int, default=1, help="Number of environments to spawn.")
15# append AppLauncher cli args
16AppLauncher.add_app_launcher_args(parser)
17# demos should open Kit visualizer by default
18parser.set_defaults(visualizer=["kit"])
19# parse the arguments
20args_cli = parser.parse_args()
21
22# launch omniverse app
23app_launcher = AppLauncher(args_cli)
24simulation_app = app_launcher.app
25
26"""Rest everything follows."""
27
28import torch
29
30import isaaclab.sim as sim_utils
31from isaaclab.assets import AssetBaseCfg, RigidObjectCfg
32from isaaclab.scene import InteractiveScene, InteractiveSceneCfg
33from isaaclab.sensors import ContactSensorCfg
34from isaaclab.utils import configclass
35
36##
37# Pre-defined configs
38##
39from isaaclab_assets.robots.anymal import ANYMAL_C_CFG # isort: skip
40
41
42@configclass
43class ContactSensorSceneCfg(InteractiveSceneCfg):
44 """Design the scene with sensors on the robot."""
45
46 # ground plane
47 ground = AssetBaseCfg(prim_path="/World/defaultGroundPlane", spawn=sim_utils.GroundPlaneCfg())
48
49 # lights
50 dome_light = AssetBaseCfg(
51 prim_path="/World/Light", spawn=sim_utils.DomeLightCfg(intensity=3000.0, color=(0.75, 0.75, 0.75))
52 )
53
54 # robot
55 robot = ANYMAL_C_CFG.replace(prim_path="{ENV_REGEX_NS}/Robot")
56
57 # Rigid Object
58 cube = RigidObjectCfg(
59 prim_path="{ENV_REGEX_NS}/Cube",
60 spawn=sim_utils.CuboidCfg(
61 size=(0.5, 0.5, 0.1),
62 rigid_props=sim_utils.RigidBodyPropertiesCfg(),
63 mass_props=sim_utils.MassPropertiesCfg(mass=100.0),
64 collision_props=sim_utils.CollisionPropertiesCfg(),
65 physics_material=sim_utils.RigidBodyMaterialCfg(static_friction=1.0),
66 visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.0, 1.0, 0.0), metallic=0.2),
67 ),
68 init_state=RigidObjectCfg.InitialStateCfg(pos=(0.5, 0.5, 0.05)),
69 )
70
71 contact_forces_LF = ContactSensorCfg(
72 prim_path="{ENV_REGEX_NS}/Robot/LF_FOOT",
73 update_period=0.0,
74 history_length=6,
75 debug_vis=True,
76 filter_prim_paths_expr=["{ENV_REGEX_NS}/Cube"],
77 )
78
79 contact_forces_RF = ContactSensorCfg(
80 prim_path="{ENV_REGEX_NS}/Robot/RF_FOOT",
81 update_period=0.0,
82 history_length=6,
83 debug_vis=True,
84 filter_prim_paths_expr=["{ENV_REGEX_NS}/Cube"],
85 )
86
87 contact_forces_H = ContactSensorCfg(
88 prim_path="{ENV_REGEX_NS}/Robot/.*H_FOOT",
89 update_period=0.0,
90 history_length=6,
91 debug_vis=True,
92 )
93
94
95def run_simulator(sim: sim_utils.SimulationContext, scene: InteractiveScene):
96 """Run the simulator."""
97 # Define simulation stepping
98 sim_dt = sim.get_physics_dt()
99 sim_time = 0.0
100 count = 0
101
102 # Simulate physics
103 while simulation_app.is_running():
104 if count % 500 == 0:
105 # reset counter
106 count = 0
107 # reset the scene entities
108 # root state
109 # we offset the root state by the origin since the states are written in simulation world frame
110 # if this is not done, then the robots will be spawned at the (0, 0, 0) of the simulation world
111 root_pose = scene["robot"].data.default_root_pose.torch.clone()
112 root_pose[:, :3] += scene.env_origins
113 scene["robot"].write_root_pose_to_sim_index(root_pose=root_pose)
114 root_vel = scene["robot"].data.default_root_vel.torch.clone()
115 scene["robot"].write_root_velocity_to_sim_index(root_velocity=root_vel)
116 # set joint positions with some noise
117 joint_pos, joint_vel = (
118 scene["robot"].data.default_joint_pos.torch.clone(),
119 scene["robot"].data.default_joint_vel.torch.clone(),
120 )
121 joint_pos += torch.rand_like(joint_pos) * 0.1
122 scene["robot"].write_joint_position_to_sim_index(position=joint_pos)
123 scene["robot"].write_joint_velocity_to_sim_index(velocity=joint_vel)
124 # clear internal buffers
125 scene.reset()
126 print("[INFO]: Resetting robot state...")
127 # Apply default actions to the robot
128 # -- generate actions/commands
129 targets = scene["robot"].data.default_joint_pos.torch
130 # -- apply action to the robot
131 scene["robot"].set_joint_position_target_index(target=targets)
132 # -- write data to sim
133 scene.write_data_to_sim()
134 # perform step
135 sim.step()
136 # update sim-time
137 sim_time += sim_dt
138 count += 1
139 # update buffers
140 scene.update(sim_dt)
141
142 # print information from the sensors
143 print("-------------------------------")
144 print(scene["contact_forces_LF"])
145 print("Received force matrix of: ", scene["contact_forces_LF"].data.force_matrix_w)
146 print("Received contact force of: ", scene["contact_forces_LF"].data.net_forces_w)
147 print("-------------------------------")
148 print(scene["contact_forces_RF"])
149 print("Received force matrix of: ", scene["contact_forces_RF"].data.force_matrix_w)
150 print("Received contact force of: ", scene["contact_forces_RF"].data.net_forces_w)
151 print("-------------------------------")
152 print(scene["contact_forces_H"])
153 print("Received force matrix of: ", scene["contact_forces_H"].data.force_matrix_w)
154 print("Received contact force of: ", scene["contact_forces_H"].data.net_forces_w)
155
156
157def main():
158 """Main function."""
159
160 # Initialize the simulation context
161 sim_cfg = sim_utils.SimulationCfg(dt=0.005, device=args_cli.device)
162 sim = sim_utils.SimulationContext(sim_cfg)
163 # Set main camera
164 sim.set_camera_view(eye=[3.5, 3.5, 3.5], target=[0.0, 0.0, 0.0])
165 # design scene
166 scene_cfg = ContactSensorSceneCfg(num_envs=args_cli.num_envs, env_spacing=2.0)
167 scene = InteractiveScene(scene_cfg)
168 # Play the simulator
169 sim.reset()
170 # Now we are ready!
171 print("[INFO]: Setup complete...")
172 # Run the simulator
173 run_simulator(sim, scene)
174
175
176if __name__ == "__main__":
177 # run the main function
178 main()
179 # close sim app
180 simulation_app.close()