Objective: to characterize the motion of and program a 6 DOF robot arm to be used as a pick and place (PnP) machine using computer vision.

6 Degree of Freedom Robot Arm

leArm.jpg

PAGE UNDER CONSTRUCTION

Specifications of LeArm

For this project I used LeArm 6 DOF robot kit as an off the shelf robot arm. It is programmable and controllable. I would like to tie it with a computer vision AI program to recognize little cubes, calculate their coordinates, move to that position to grab the cube, and then place the cube in a little basket.

Below are the details and specifications for LeArm.

ADD DETAILS HERE

Denavit-Hartenberg Frames and Coordinate Systems

To begin, the first thing is to understand and learn D-H frames and coordinate systems for mechanisms.

Below is text taken from automaticaddison describing D-H coordinate systems and their rules. You can find the full article here. I suggest you read take a look as it is very detailed, and valuable information to know.

Denavit-Hartenberg (D-H) frames help us to derive the equations that enable us to control a robotic arm.

The D-H frames of a particular robotic arm can be classified as follows:

  • Global coordinate frame: This coordinate frame can have many names…world frame, base frame, etc. […]
  • Joint frames: We need a coordinate frame for each joint.
  • End-effector frame: We need a coordinate frame for the end effector of the robot (i.e. the gripper, hand, etc….that piece of the robot that has a direct effect on the world).

The other important information to know about D-H coordinate frames are the four rules for defining the D-H convention in a mechanical system and kinematic drawing. These rules are important to ensure that a 6 DOF robot is properly defined and easily programmable. Again the following text is taken directly from the automaticaddison.com article.

Here are the four rules that guide the drawing of the D-H coordinate frames:

  1. The z-axis is the axis of rotation for a revolute joint.
  2. The x-axis must be perpendicular to both the current z-axis and the previous z-axis.
  3. The y-axis is determined from the x-axis and z-axis by using the right-hand coordinate system.
  4. The x-axis must intersect the previous z-axis (rule does not apply to frame 0).

Below is an example for how to draw the D-H frames for a 3 linkage mechanism with revolute joints.

dhcoords.jpg

Next step is to draw and define the D-H frames for LeArm so that we can begin to program and manipulate it.

I followed this guide at the following link: ulitmate guide to 6DOf robot