Retractable antennas are commonly used in mobile telecommunication equipment such as portable telephones, cellular phones and two-way radios. Typically, retractable antennas used in mobile telecommunication instruments require two-handed operation for extension. For example, when answering a call on a cellular phone, the user must open the flip-open cover, if so equipped, pull out the antenna with one hand while holding the phone in the other hand, push a button to answer the call, then speak. This multiple step operation is cumbersome, particularly if the user is carrying another article or is otherwise impaired from using both hands to extend the antenna.
Several arrangements have been proposed for powering the extension of the antenna on small, mobile telecommunication instruments. Electrically powered, motor driven antenna extenders, such as those found on vehicles and larger communication instruments, are undesirable for small instruments because of the space requirements for the motor and drive mechanisms, the resultant added weight and cost, and the significant current draw on a limited power source, i.e., the batteries of the instrument.
Other arrangements have also been proposed for the automatic extension of antennas for mobile telecommunication instruments. For example, a guided helical compression spring arrangement is disclosed in co-pending application Ser. No. 08/627,448, filed Apr. 14, 1996 by Charles A. Rudisill for a RETRACTABLE ANTENNA ASSEMBLY, and assigned to the Assignee of the present invention. Other linear or variable rate springs, such as helical extension springs, have also been proposed for use in antenna extension systems. However, spring extension systems using either linear or variable rate springs apply a significantly higher bias force on an antenna when it is deflected than when it approaches its free length. For example, if an antenna is biased at the extended position with a minimal preload spring force, the force acting on the antenna when retracted will be the product of the spring rate times the deflection of the spring, plus the preload force. The resultant high bias force produced by such springs causes the antenna, when released, to extend very rapidly, virtually instantaneously. If the user is careless, the rapidly extending distal end of the antenna could strike an object or person, perhaps even in the eye, and cause serious damage or injury.
The present invention is directed to overcoming the problems set forth above. It is desirable to have an extension system for the antenna on mobile telecommunication instruments that is small, lightweight, economical to produce, and does not require an auxiliary power source for its operation. It is also desirable to have such an extension system that automatically extends the antenna at a predetermined controlled velocity, upon actuation of a release latch.