How to measure actuation force

Actuation force testing measures the force needed to activate various products and components, ranging from consumer dispensers to medical devices. It plays a critical role in product design, quality control, and safety across multiple industries. For example, manually actuated spray pumps and dispensers, such as for hair fixatives, air fresheners, or liquid soaps, depend on the consumer to generate the required pressure for operation. As dispenser designs evolve, especially for child-friendly products, ensuring ease of use is crucial. Children, for instance, may struggle to apply enough force to a pump, causing it to malfunction or tip over. An actuation force test uses a hemispherical probe to simulate and assess such scenarios.

In medical devices, actuation force testing is essential. Metered-dose inhalers (MDIs), which deliver precise doses of medication to the lungs, require regular testing to ensure reliability, particularly for patients with low physical strength during critical moments. The performance of the metering valve, a crucial component, must be tested to ensure compatibility with various drug formulations.

Actuation force testing also applies beyond product dispensing. Here are some example applications using a Texture Analyser:

• Switch and button actuation: In electronics, measuring the force needed to press buttons on devices such as remote controls, keyboards, and touchscreens ensures a consistent user experience. For example, testing the actuation force of a computer keyboard key to ensure uniform typing feedback.
• Latch and lock mechanisms: Testing the force required to engage or disengage locks in doors, cabinets, and cars guarantees ease of use and security. For example, measuring the actuation force needed to open a car door handle or a safety latch.
• Valve and faucet/tap testing: In plumbing, measuring the force to operate faucets or valves ensures user comfort and product longevity.
• Medical device testing: Testing devices like insulin pens, syringes, and inhalers ensures they deliver precise doses with minimal effort/force.
• Automotive component testing: Testing controls such as steering wheel buttons and brake pedals ensures driver safety and comfort.
• Safety feature testing: Ensuring safety mechanisms, like seatbelt buckles and airbags, activate with the appropriate force during emergencies.
• Spring actuation force testing: Testing the force to compress or extend springs in mechanical systems ensures proper functionality.
• Circuit breaker testing: In electrical systems, ensuring the proper force is required to engage or disengage circuit breakers for safe operation.
• Emergency stop button testing: Ensuring that emergency stop buttons in industrial machinery require appropriate force to prevent accidental activation.

In each of these examples, a Texture Analyser applies a controlled force/distance while measuring the distance/force required for actuation. These measurements provide valuable insights for product design and quality control, ensuring components function as intended across various industries.

In a typical actuation test, a hemispherical/spherical probe is usually used to simulate the pressing action on a button or pump simulating a finger. The sample is located under the probe which pushes against it as the Texture Analyser records the force and distance throughout the test beyond the actuation point.

Imitative actuation test using a 1/2" ⌀ Hemispherical Probe.

Imitative test of inhaler actuation using an Inhaler Support Rig.

• Temperature: Temperature can significantly influence the physical properties of materials, affecting their hardness, consistency, and overall delivery behaviour during actuation force measurements.
• Humidity: Humidity levels can impact the moisture content of samples, potentially altering their texture and mechanical properties, which in turn affects the actuation force required.
• Compression speed: The rate at which force is applied during testing can influence the measured actuation force, as materials may respond differently to varying speeds of compression. The chosen speed should remain constant for comparison purposes.
• For dispensers: The specific design of a dispenser, along with the internal pressure and consistency of its contents, directly influences the force required for actuation and product delivery.
• For inhalers: The valve design, propellant system, and drug formulation in inhalers are critical factors that determine the actuation force needed to deliver a precise, reproducible dose of medication.
• For electronic buttons: The switch mechanism and tactile feedback design of electronic buttons play crucial roles in determining the actuation force required and the user's perception of button press quality.

The Stable Micro Systems Texture Analyser excels in optimising actuation force measurements due to its combination of high precision, wide choice of probes to imitate finger action, and  a wide test speed range to simulate various actuation scenarios.

Exponent Connect software provides comprehensive analysis of actuation characteristics, including pre-travel, tactile force, and actuation points. This versatility and precision make it an ideal tool for testing a wide range of products with actuation mechanisms, from auto-injectors to keyboard keys, enabling researchers and manufacturers to fine-tune product performance with unparalleled accuracy.