Kino Gripper

3D printed Kino gripper repository/ROS package.

Kino, from the greek κίνημα kinema ("movement, motion"), is an adaptative gripper using a Dynamixel AX-12A servomotor as actuator. It leverages the abilies of the smart servomotor: compliance, possibility to set torque, velocity... Communication with the servomotor is handled with an integrated USB2AX. Power is provided by a DC-DC buck converter.

The gripper is designed to be mounted on a HEBI Robotics Arm but can easily be modified to be mounted on other arms.

Assembly instructions can be found here.

Features

Gripper mount

The gripper is designed to be mounted on a HEBI Robotics arm.

Screw the base attachement part to the output shaft of the HEBI actuator.

Connect with the main part of the gripper.

Slide the main part of the gripper, being careful not to damage the USB connector. Screw the main part in place

Compliance

Torque and position compliance is provided by the servomotor. The compliance values can be set according to the Dynamixel AX-12A documentation.

Adaptive grip

Thanks to the spring on each finger, the gripper can fold to encircle small objects. The spring can be changed to allow for easier/harder finger deformation.

Changeable finger tips

Finger tips can be change by simply unscrewing/screwing.

Three finger tip types are provided, but more can easily be designed:

• Default, with zig-zag pattern
• Thin pads, to be printed and completed by gluing a thin rubber pad
• Thick pads, to be printed and completed by gluing a thick foam pad

Installation

The gripper package can be used as a ROS or C++ package.

Dependencies

• Robot Operating System (ROS)
• Dynamixel SDK. Either through ROS package or direct install.

Building

To build the package, clone the current repository in your catkin workspace and build it.

cd catkin_ws/src
git clone https://github.com/RBinsonB/kino_gripper.git

Build your workspace with either catkin_make or catkin build

cd ...
catkin_make

Usage

ROS Node

The gripper ROS node can be launched using the following command. Don't forget to set the appropriate port, device ID and baudrate parameters beforehand.

rosrun kino_gripper kino_gripper_node

Subscribed Topics

• gripper_cmd (control_msgs/GripperCommand)

  Gripper command message. The position field is commanded distance between the fingers. Torque command is not taken into account and the default servomotor torque will be used.

Parameters

• ~port (string, default: "/dev/ttyACM0")

  Servomotor port. For more information check about USB2AX and AX-12A Dynamixel servomotor.

• ~baudrate (int, default: 1000000)

  Servomotor baudrate in bps. For more information check about USB2AX and AX-12A Dynamixel servomotor.

• ~device_id (uint8_t, default: 1)

  Servomotor ID. For more information check about AX-12A Dynamixel servomotor.

C++

The gripper library can be used independently of ROS. To do so, include the appropriate header in your file.

#include <kino_gripper.h>

To use the gripper, you can create a gripper object using:

KinoGripper(int device_id, char const* device_name, int baudrate)

The gripper can then be closed or opened using the Close() and Open() functions. Example:

KinoGripper gripper(1, "/dev/ttyACM0", 1000000);

gripper.Close(40.0);              // Close fingers to 40mm
while (!gripper.IsClosed()){ };   // Wait for gripper to finish
gripper.Close(0.0);               // Close fingers to 0mm
while (!gripper.IsClosed()){ };
gripper.Open();                   // Open gripper completely
while (!gripper.IsClosed()){ };

API

Public Member Functions

KinoGripper(int device_id, char const* device_name, int baudrate)
  Gripper object constructor.
  Parameters : 
      device_id Dynamixel servomotor device ID
      device_name Dynamixel servomotor port
      baudrate Dynamixel servomotor baudrate in bps

void InitGripper()
  Initializes the gripper servomotor and build lookup table for position command

bool Close(float distance)
  Close the gripper to the given distance (between fingers)
  Parameters : 
      distance Distance between fingers in mm
  Returns :
      True if command sent successfully to servomotor

bool Open()
  Open the gripper fully by sending maximum angle command (can be set SetMinMaxAngle())
  Returns :
      True if command sent successfully to servomotor

bool IsClosed()
  Check if the gripper is closed at the value commanded via Close(), uses an inner hardcoded threshold.
  Returns :
      True if gripper is closed to the last commanded value

bool IsMoving()
  Check if the gripper is moving.
  Returns :
      True if gripper is currently in motion

bool SetSpeed(uint16_t speed)
  Set servomotor rotation speed
  Parameters : 
      speed Servomotor rotation speed in rev/min
  Returns :
      True if operation is successful

bool SetMinMaxAngle(uint16_t min_angle, uint16_t max_angle)
  Set servomotor minimum and maximum angles
  Parameters : 
      min_angle Minimum servomotor angle in steps
      max_angle Maximum servomotor angle in steps
  Returns :
      True if operation is successful

bool SetCompliance(uint8_t cw_margin, uint8_t ccw_margin, uint8_t cw_slope, uint8_t ccw_slope, uint16_t punch)
  Set servomotor compliance parameters. For more information, check Dynamixel AX-12A control table for more details.
  Parameters : 
      cw_margin Clockwise compliance margin in deg 
      ccw_margin Counter-clockwise compliance margin in deg
      cw_slope Clockwise compliance slope
      ccw_slope Counter-clockwise compliance slope
      punch Punch
  Returns :
      True if operation is successful

License

All rights reserved