Framework’s messages and action

In addition to the classic ROS messages and actions, the framework supports some home made messages and action that can be used in your scripts. We also provide some handful methods that allow to create some messages easily in order to avoid boilerplate. All the messages can be found in this folder and the action can be found here.

TorqueIntensity

This message contains the information required to squeeze. As a matter of fact, it exists some two-steps controller for grasping. The first one is to use position controller (for instance) to actuate the joints to a specific state. Once the latter is reached, torque is applied to some joints. The name of such joints must be specified in joint_names. Since each joint can apply a different percentage of max_torque, the value (between -1 and 1) corresponding to each joint must be specified in torque_intensity. A negative value would mean motion in the outward direction for instance.

ManipulatorState

This message fully describes the state of the manipulator. It contains a field posture which is a JointState describing the internal state of the manipulator. It also contains the field pose which describes with a PoseStamped the pose of the manipulator.
We believe that this information allow to specify the state of the manipulator regardless of the application.

StandardisedGrasp

The definition of a grasp differs greatly from one work to another. We propose here a quite generic definition of a grasp. Since you can use only some of the fields contained in this message, we believe that this message can be compatible with most of the different works about grasping.
In our definition, a grasp can be characterised by:

  • grasp_id: String that can be used to name the given grasp. Especially useful when stored in a database.
  • hand_id: String that specifies for which manipulator the grasp has been created. Useful when storing messages in a database.
  • object_id: String specifying for which object the grasp has been generated. Especially useful when grasping known or familiar objects. Can also be used to do a query in a database.
  • pregrasp: ManipulatorState message that contains how should be the manipulator before grasping. Can be filled with an empty ManipulatorState message.
  • grasp: ManipulatorState message containing how the manipulator should be for grasping an object. Can be filled with an empty ManipulatorState message.
  • postgrasp: ManipulatorState message containing how the manipulator should be for after grasping an object. It can be seen as the release state. Can be filled with an empty ManipulatorState message.
  • torque_intensity: TorqueIntensity message that contains how the manipulator should behave when a two-steps controller is used. Can be filled with an empty TorqueIntensity message.
  • grasp_quality: Float estimating the probability of success of the given grasp. This value highly depends on the task carried out, and to the metric being used. These choices is left to you. Can be 0.

As you can see, most of the methods generating grasps provide at least some of the information contained in this message. That is why with some simple modification we can easily make it compatible with most of the methods.

GraspCommand

This message contains all information required to execute a grasp. In addition to the StandardisedGrasp message, it contains the grasp state (which phase should be executed next) as well as the maximum torque the manipulator should deploy. Having the grasp state allows to use the same grasp message to execute three different manipulator states by just changing its value.

Grasp action

The provided action server dedicated to grasping relies on this action. The goal definition is the GraspCommand message. Its result is a set of three booleans that must be returned stating whether the grasp state defined in the goal has correctly been executed. We defined the feedback as the joint state of the manipulator. You can find an example of action server here and here.

Utils

We provide some function both in python and in C++ in order to help you create some standard and widely used ROS messages and some of the aforementioned messages.
You can for instance find a C++ function creating a StandardisedGrasp message for you from a set on input parameters. The python equivalent can be found here. You also have a set of handful functions taking care of creating standard messages such as PoseStamped, and JointState.