Principle:ARISE Initiative Robosuite Gripper Control Abstraction
| Knowledge Sources | |
|---|---|
| Domains | Robotics, Manipulation, Software Architecture |
| Last Updated | 2026-02-15 07:00 GMT |
Overview
The gripper control abstraction defines a base interface for gripper controllers and a simple proportional grip implementation, enabling uniform gripper command processing regardless of gripper morphology.
Description
Grippers are the end-effector actuators that enable a robot to grasp and manipulate objects. They vary widely in morphology: parallel-jaw grippers have two symmetric fingers, multi-finger hands have numerous independently controllable digits, and specialized grippers may have suction or adhesion mechanisms. Despite this diversity, the control interface can be abstracted into a common pattern: accept a grip command (typically a scalar value between fully open and fully closed) and produce the actuator signals needed to achieve that grip state.
The gripper controller base class mirrors the arm controller base class in structure but is specialized for gripper-specific concerns. It tracks gripper joint positions, velocities, and actuator indices (which may differ from joint indices when the gripper uses tendon-driven or underactuated mechanisms). It provides the standard action-scaling, state-update, and torque-clamping infrastructure. The abstract run_controller and set_goal methods define the contract for subclasses.
The simple proportional grip implementation maps a single scalar action (ranging from -1 for fully open to +1 for fully closed, or vice versa) to actuator commands via linear scaling. All fingers move in unison, driven by the same command. The scaled command is mapped to the actuator control range using bias and weight computed from actuator limits, producing position or velocity commands that the simulator's actuator model interprets. This simple approach is sufficient for parallel-jaw grippers and provides a baseline for more complex gripper control schemes.
Usage
Apply the gripper control abstraction whenever grippers must be controlled uniformly across different robots and gripper types. The base class is suitable for any new gripper controller implementation, while the simple proportional grip is the default choice for parallel-jaw grippers in manipulation tasks. For dexterous hands requiring independent finger control, a more sophisticated subclass would extend the base while maintaining the same interface.
Theoretical Basis
Gripper Controller Architecture:
Base Class (GripperController):
- Tracks: joint_pos, joint_vel, actuator_index
- Provides: scale_action(), update(), clip_torques()
- Abstract: run_controller(), set_goal()
Simple Grip Implementation (SimpleGripController):
Input: action in [-1, 1] (scalar grip command, broadcast to all actuators)
1. Scale action from input range to output range:
scaled = scale_action(action)
2. Map to actuator control range:
ctrl_range = [actuator_min, actuator_max]
bias = 0.5 * (ctrl_max + ctrl_min)
weight = 0.5 * (ctrl_max - ctrl_min)
output = bias + weight * scaled
3. Return output as actuator commands
Control dimension = number of actuators (not joints)
All actuators receive the same scaled command
Key design decisions:
- Actuator vs. joint indexing: Grippers may have more joints than actuators (underactuated/tendon-driven), so the controller tracks both actuator and joint indices separately. The control dimension is based on actuators, not joints.
- Unified command: The simple grip controller broadcasts a single scalar to all actuators, which is appropriate for symmetric grippers where all fingers should move together.
- Action scaling toggle: An optional flag allows disabling action scaling, which is useful when the commanding agent already produces correctly-scaled commands.
- Separate hierarchy from arm controllers: Grippers have distinct concerns (no Jacobians, no mass matrix, direct actuator mapping) warranting their own base class rather than sharing with arm controllers.