Keypad Actuation Profiles
Increasing miniaturization of mobile phones means that the alpha numeric keypads used for number dialing and data entry are also becoming smaller. These keypads must be tested to ensure that they are easy enough to use. One measure of this performance is the activation force and profile of individual keys on the keypad. The force required to activate the key should be sufficiently low that the key is easy to press, considering that the phone may be operated by, for example, the elderly. However, the force should not be so low that accidental key presses are likely, for example when the phone is carried in a pocket or handbag.
A basic system for keypad testing comprises of a universal testing machine, equipped with a low capacity load cell, and a chuck fixture holding a steel prong. Additionally, a platen or t-slot table is used to support the phone or keypad module. During the test, the load profile, and sometimes the displacement characteristic of the key press, are monitored.
For more detailed information, the electrical contact can be wired into the test system, providing precise determination of the switch closure position and force. In order to provide accurate data, a system with a high data logging rate should be used, so that rapid changes in force which occur over very small distances at switch closure can be observed. In addition, the system used should have high position accuracy and control to avoid damage to delicate components.