Effort Sensor

The effort sensor in NVIDIA Isaac Sim tracks the torque or force applied to individual joints. Torque is measured for revolute joints and magnitude of force is measured for linear joints.

See the Isaac Sim Conventions documentation for a complete list of NVIDIA Isaac Sim conventions.

GUI

Scene Setup

Begin by adding a Simple Articulation to the scene, which can be accessed via Isaac Sim Asset.

1. Open the Isaac Sim Assets and search for simple_articulation

2. Drag simple_articulation onto the World prim in the Stage UI window on the right hand side to add an instance into the environment.

3. To drive the revolute joint, in the Stage window, select the RevoluteJoint prim at /World/simple_articulation/Arm/RevoluteJoint, and scroll down to Drive in the Property window. Set the target velocity to 90 deg/s, and stiffness to 0.

Creating and Modifying the Effort Sensor

The following section describes how to create the effort sensor via the Script Editor, opened from Window -> Script Editor. The effort sensor can be created using the isaacsim.sensors.physics.EffortSensor Python wrapper class. The benefit of using the wrapper class is that it comes with additional helper functions to set the effort sensor properties and retrieve sensor data.

from isaacsim.sensors.physics.scripts.effort_sensor import EffortSensor
import numpy as np

sensor = EffortSensor(
    prim_path="/World/simple_articulation/Arm/RevoluteJoint",
    sensor_period=0.1,
    use_latest_data=False,
    enabled=True
)

To modify sensor parameters, you can change class member variables like sensor_period, use_latest_data, and enabled directly, and for changing the dof_name and buffer_size for the readings, please use the corresponding member functions update_dof_name and change_buffer_size.

Reading Sensor Output with Python

get_sensor_reading(self, interpolation_function = None, use_latest_data = False)

the get sensor reading function takes in two parameters: an interpolation function (optional) to use in place of the default linear interpolation function, and use latest data flag (optional) for retrieving the data point from the current physics step if the sensor is running at a slower rate than physics rate. The function will return an EsSensorReading object which contains is_valid, time, and value.

After you created the effort sensor, press PLAY to start the simulation, and call the function below to get the sensor reading for the current frame.

from isaacsim.sensors.physics.scripts.effort_sensor import EffortSensor

# get sensor reading
reading = sensor.get_sensor_reading(use_latest_data = True)

Sample usage with custom interpolation function:

from isaacsim.sensors.physics.scripts.effort_sensor import EffortSensor

# Input Param: List of past EsSensorReading, time of the expected sensor reading
def interpolation_function(data, time):
    interpolated_reading = EsSensorReading()
    # do interpolation
    return interpolated_reading

# get sensor readings
reading = sensor.get_sensor_reading(interpolation_function)

OmniGraph Workflow

Now let’s set up the OmniGraph to create the effort sensor and collect readings from it.

1. Create the new action graph by navigating to Window > Graph Editors > Action Graph, and selecting New Action Graph in the new tab that opens.

2. Now add the following nodes to the graph:

   • On Playback Tick: Executes the graph nodes every simulation timestep.

   • Isaac Read Effort Node: Reads the effort sensor. In the Property tab, set Effort Prim to the exact joint of measurement. For example /World/simple_articulation/Arm/RevoluteJoint in simple_articulation.usd.

   • To String: Converts the effort sensor readings to string format.

   • Print Text: Prints the string readings to console. In the Property tab, set Log Level to Warning so that messages are visible in the terminal/console by default. Additionally, check To Screen to print directly to screen.

Connect the above nodes as follows to print out the effort sensor reading:

Note

Remember to configure the joints to the correct axis to get the expected readings!

API Documentation

See the API Documentation for complete usage information.