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Chapter 03

Work Envelope Basics

Page 1

This Chapter covers the following topics:
  1. Work Envelope Basics
  2. Robot Joint Movement Configuration
  3. Selecting a Configuration for TL-RAM-2

Simply speaking a robot's work envelope is its range of movement.

   It is the shape created when a manipulator reaches forward, backward, up, down, right, left and any other direction it is free to move. These distances are determined by the length of a robot's arm, the structure and orientation of its axes. Each axis contributes its own range of motion. A robot can only perform within the confines of this work envelope. Hence it is important to understand it.

Work Envelope: In mechanical engineering, an envelope is a solid representing all positions which may be occupied by an object during its normal range of motion.

   In robotics, the working envelope or work area is the volume of working or reaching space. Some factors of a robot's design (configurations, axes or degrees of freedom) influence its working envelope.

   In order to proceed with mathematical calculations for robot motion, the concept of the Robot's Work Envelope must be well understood. Since, the robot's base is fixed at the origin of the co-ordinate system, its links have fixed lengths and the link joints have angular movement limits, the gripper tip is confined to reach a limited region only.

   So, if someone commands the gripper to reach a destination point, it must be checked that the point lies inside the work-envelope. If the point lies outside the envelope, then it is termed as un-reachable point. Otherwise, if the point lies inside the work-envelope then further calculations can be done. The calculations are like: How much degrees Link-1 and Link-2 are to be moved in order to reach the destination point (Inverse kinematics).

The work envelope of the robot depends on various factors, some of them are:
  1. Angular movement limits: Just like all the human arm joints can't move full 360, the robot's joints also have angular rotation limits. The servo motor powering the robot arm joints usually have a limit of 180 angular rotation. Different types of servo motors have different angular rotation limitations. In this tutorial (and the project) the servo motors have a limit of 180 degree rotation.
  2. Orientation of joint motors: The same set of robot motors can be mounted on the robot arm joints in different configurations resulting in different work envelopes.
  3. Link Lengths and their ratios: The first thing which comes to mind is longer the arms (links), longer the reach (limit). But, that's not everything ratio also matters, the length of each link.

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