Stiction

Stiction refers to the static friction that must be overcome to initiate the relative motion between two stationary surfaces in contact. It's a critical concept in engineering, particularly in the design of moving parts within machinery. This initial resistance to movement, higher than the subsequent dynamic (kinetic) friction, results from the interlocking of surface asperities, adhesion due to intermolecular forces (like van der Waals forces), and the presence of contaminants or lubricants. stiction creates a 'stick-slip' phenomenon where movement occurs in abrupt jumps rather than a smooth, continuous flow. Understanding and mitigating stiction is paramount for achieving precise control, reducing wear and tear, and improving the overall efficiency of mechanical systems. The magnitude of stiction depends on factors such as surface roughness, the applied normal force, the materials involved, and environmental conditions.

Stiction meaning with examples

• The robotic arm's movement was jerky due to stiction in its joints. Engineers redesigned the joints, using smoother materials and improved lubrication, to reduce the stiction. The initial static friction was proving problematic to controlling precise movements. This caused inaccurate placement of the arm, preventing it from completing the assigned task accurately and efficiently.
• In micro-electromechanical systems (MEMS), stiction is a major concern. The tiny components can be rendered non-functional by stiction forces, which prevents them from being released. Manufacturers employ techniques like surface treatment and anti-stiction coatings to overcome this issue and increase component lifespan. This helps to ensure reliability and prolong the systems utility.
• The old printer had significant stiction in its paper feed mechanism, causing frequent paper jams. The friction between the feed rollers and the paper caused too much resistance to overcome without a significant push. Regular cleaning and the application of a specialized lubricant were needed to alleviate the stiction. Otherwise, the process became significantly more cumbersome.
• A precision instrument suffered from stiction in its fine adjustment knobs. The stiction made it hard to make small, incremental adjustments to its sensitive components. A combination of lubrication and design modifications proved to be effective at improving the instrument's performance and enhancing the user experience. This ensured more precise and accurate measurements could be performed.