Chapter 19 of Introduction to Robotics by Phillip John McKerrow is far more than a catalog of gripper designs; it is a treatise on the interface between cybernetics and mechanics. It reminds the reader that the utility of a robot is defined by its ability to perform tasks. Whether through the detailed analysis of friction forces required to hold a bowling ball versus an egg, or the discussion of sensory feedback required for delicate assembly, the chapter grounds the high-level theory of robotics in the gritty reality of hardware. For any student or practitioner looking to understand how robots actually "do" work, this chapter is an indispensable guide to the design and selection of end-effectors. Voovi Unrated Web Series Upd Optimized Productive
Perhaps the most forward-looking aspect of McKerrow’s treatment of end-effectors in this chapter is the integration of sensors. He argues that an "open-loop" gripper—one that simply closes until it hits a hard stop—is insufficient for intelligent robotics. He details the necessity of tactile sensors and force/torque sensing . Ssis-334 [WORKING]
Introduction In the study of robotics, there is a frequent tendency to focus heavily on the mechanics of the arm itself—kinematics, dynamics, and trajectory planning. However, a robot arm without a means of interacting with its environment is merely a complex machine performing a dance in empty space. In Introduction to Robotics , Phillip John McKerrow addresses this critical component in Chapter 19 (typically titled "End-Effectors" or "Grippers and Tools"). This chapter serves as a bridge between the theoretical mathematics of robot control and the practical realities of industrial application. It provides a comprehensive taxonomy of the "hand" of the robot, exploring the mechanics, drive systems, and sensory requirements necessary to manipulate the physical world.
A significant portion of Chapter 19 is dedicated to the mechanics of gripping. McKerrow provides a rigorous analysis of the forces required to hold an object. He introduces the physics of friction and the concept of the "friction cone," explaining how the coefficient of friction between the gripper pads and the object dictates the necessary gripping force to prevent slipping.
The text explains how simple contact switches can signal the presence of an object, while more advanced arrays can determine the shape of an object or detect slip. The concept of "compliance" is also introduced. When a robot inserts a peg into a hole, a rigid gripper will likely jam. McKerrow explains the "Remote Center Compliance" (RCC) device, a mechanical solution that allows the end-effector to correct small positional errors passively, a vital concept in automated assembly that bridges the gap between the robot's rigid structure and the imperfect real world.
This distinction is crucial because it dictates the design philosophy. A gripper must conform to the object being held, requiring considerations of friction, center of gravity, and inertia. A tool, however, must be positioned accurately relative to the workpiece, requiring the robot to act as a rigid, precise guide. McKerrow’s text excels in detailing the mechanical variations within the gripper category, outlining the differences between parallel jaw, angular, and multi-fingered designs, each suited to specific geometric constraints.
McKerrow begins the chapter by establishing a fundamental classification system for end-effectors. He distinguishes between two primary categories: grippers and tools . Grippers are designed to hold objects, effectively making the robot a material-handling device. Tools, conversely, are mounted directly to the wrist to perform work on the environment, such as welding torches, spray guns, or grinding wheels.