Configure Grasp Planner

Tweaking Grasp Pose Generation

The grasp pose generation is very simple. In the object frame, a three-dimensional spline is defined along the handle (via config). At each point along this spline, a particular orientation is chosen (according to a policy) creating a valid pose for the "tool" frame of the robot. The tool frame is an imaginary frame fixed relative to the robot's wrist where the handle should rest in the gripper. There are some additional policies related to sampling and prioritizing poses along the spline but otherwise that's all there is to it.

The grasp poses are optionally filtered with respect to the existence of kinematics solutions and visibility constraints. Currently, the reposition planner and grasping pipeline separately handle filtering generated grasps. Both modules share the same visibility checker, which checks for visibility against an imaginary AR tag located at some offset relative to the wrist.

The arm motion to get to the grasp pose is split into two parts: a planned motion to a pre-grasp pose, and a motion from the pre-grasp pose to the grasp pose. The offset between the pre-grasp and the grasp pose is a scalar quantity representing the distance along the tool frame's x-axis (more on frame conventions later).

The parameters one can modify are specified in @rcta/config/planning/gascan_grasping.yaml@.

gas_canister_mesh_scale, degree, and control_points

These parameters define the grasping spline generated in the frame of the object. If a new gascan is ever used, these parameters need to be regenerated. Note that there is also a correction transform in the reposition planner that changes the frame of the gascan to follow certain conventions that it expects, and will also need to be changed if a new gascan is used.

wrist_to_tool_transform

This is the fixed offset, relative to the wrist of the robot, that defines the tool frame.

The orientation of the tool frame, relative to the wrist, directly affects the orientation of the gripper when a grasp pose is generated. The current convention is such that its x-axis is the direction which points towards the object, the y-axis will point along the derivative of the grasp spline, and the z-axis is chosen to produce a right-hand coordinate system. (TODO: figure)

The position of the tool frame, relative to the wrist, directly affects where the wrist should be placed relative to the grasp spline. Though nominally this is the offset required to place the tool frame along the grasp spline, the value can be modified to "calibrate" the tool frame to account for any repeatable error in the object's pose.

pregrasp_to_grasp_offset_m

This is the fixed offset, relative to the wrist frame, that defines the distance along the x-axis between the pregrasp and grasp poses.