By Dr. Jody Muelaner
Knobs are rounded handles that users can firmly and comfortably hold onto a piece of machinery or operate a control. The devices may be axisymmetric, spherical, or T-shaped.
Handles are used to transmit a force between a person’s hand and an object. A handle must have a sufficient area and ergonomic shape to transfer the force comfortably into the hand — typically through a range of angles when the handle is moved. Knobs provide this ergonomic interface.
Types of knobs include:
• Knobs: Used on levers, slideways, clamps, and screws. Knobs are often fitted to improve the ergonomics of machines that are operated or adjusted by hand. Lever arms, clamping levers, ratchet handles, crank handles, and hand wheels are all often fitted with knobs.
• Doorknob: A rounded door handle that’s typically axisymmetric and perpendicular to the face of the door. A doorknob may be fixed and used only as a means of pulling the door open, or they may rotate to operate a latch.
• Control knob: A rounded handle, often disc-shaped, which can be rotated to control machinery or electronics. Control knobs are usually attached to operate a potentiometer, a transistor that serves as a variable resistor. They are found in household applications, such as electrical cookers, heaters, and amplifiers.
• Joystick control knob: A rounded handle at the end of a stick that can be tilted in at least two axes to control a computer or machinery. Joystick control knobs are often used with digital electronic systems but it may also directly control hydraulics.
• Brodie knob or wheel spinner: A round knob that is attached to the outside of another wheel, but is able to rotate freely. It can be gripped while the larger wheel is rotated. These knobs are occasionally used on steering wheels (particularly for forklifts), and used on wheels to rotate lead screws.