Patent Publication Number: US-6215391-B1

Title: Variable frequency buzzer assembly

Description:
BACKGROUND OF THE INVENTION 
     This invention is directed to a buzzer assembly for use in a personal communications device which changes geometry in order to emit sounds at a variety of frequencies at an approximately constant volume, such as for playing melodic alerts. 
     Personal communications devices, such as cellular phones or pagers, typically have a number of components which help to alert the user to various conditions. For instance, an alert may be generated in response to an incoming call or page. The most common alert generating components are vibrators and buzzers, of which buzzers are of interest for the present invention. 
     Typically, buzzers resonate at a ring frequency around three kilohertz, producing a simple monotone alert sound or a dual tone of closely spaced frequencies. Problems arise when, instead of a simple monotone, users desire alert sounds to be other than monotone or tightly spaced dual tone, such as a melody that varies frequency over the range from about 1 kHz to about 4 kHz. Typically, buzzers are configured for optimum audio output at a particular frequency (the “ring frequency”). When such a buzzer is used at other frequencies, the buzzer output volume drops off significantly, even at frequencies as close as 200 Hz away from the ring frequency. This results in an unrecognizable melody with significant disparities in volume while the “melody” is played. This variability in loudness reduces the perceived quality, can be annoying to the user, and may result in missed calls. 
     The immediately apparent solution of using a larger buzzer capable of generating sufficient volume at different frequencies is not practical due to the extreme space constraint pressures present in today&#39;s world of ever shrinking personal communications devices. 
     It is known in the art to combine a vibrator, speaker and buzzer into one unit, called a multi-mode actuator. While such multi-mode actuators can be used to play melodies, they suffer from a serious drawback. The output from the multi-mode actuator in speaker mode should be directed into the user&#39;s ear for optimum performance. However, because the audio volume in call alert mode is much higher than in speaker mode, the output of the multi-mode actuator should not be directed into the user&#39;s ear. Thus, the optimum output routing configuration for the multi-mode actuator is different for its different functions, thereby defeating its combinational advantage. As such, it is common to use a separate buzzer whose output is typically vented perpendicular to the plane of the speaker that is used to output audio signals from the personal communications device. In this manner, the output from the buzzer is not directed into the user&#39;s ear in the event a user places the device against their ear immediately prior to an alert. However, due to existing buzzers&#39; inherent output audio volume variation over frequency, as mentioned above, existing buzzers perform poorly when asked to play melodies, rather than a monotone, for alert signals. 
     As such, there remains a need for an improved buzzer assembly for use with portable communications devices that produces an acceptable level of audio volume across a broader frequency range, so as to be able to play melodies and the like for alert signals. 
     SUMMARY OF THE INVENTION 
     The buzzer assembly of the present invention includes a combined gasket and buzzer that change geometry and thereby change acoustic impedance at different audio frequencies. The change in acoustic impedance or acoustic load of the buzzer diaphragm changes the resonant frequency of the buzzer assembly. When the buzzer is then operated at or near resonant frequency corresponding to the then-current acoustic impedance, the sound generated by the buzzer assembly is louder. By changing the resonant frequency of the buzzer assembly in this manner to correspond to the frequency of the tone to be generated, the sound volume generated by the buzzer assembly can be augmented across a frequency range that may be 3 kHz or larger. When augmented in such a fashion, the audio output from the buzzer assembly is approximately constant across a larger frequency range than with conventional buzzer solutions, and preferably across the entire range frequency range of 1 kHz to 4 kHz. 
     One preferred embodiment of the buzzer assembly includes a conventional buzzer slidably mounted in a set of guide rails. A translational actuator, in this case a solenoid, is operatively connected to the buzzer so as to slide the buzzer within the guide rails. The output port of the buzzer is sealed against an expandable buzzer gasket which is also sealed against the output port of the communications device. By moving the buzzer with the solenoid, the volume of air within the expandable buzzer gasket changes, thereby changing the acoustic impedance seen by the buzzer. This change in acoustic impedance effectively changes the resonant frequency of the buzzer and allows different frequencies to be created by the buzzer assembly at comparable audio volume levels. The mechanical action of the solenoid is controlled by a suitable control circuit that interfaces with the balance of the personal communications device to cause the buzzer assembly to create alert signals that are melodies or the like, based on stored instructions. By dynamically changing the current acoustic impedance of the buzzer, and therefore the current resonant frequency of the buzzer, to correspond to the desired audio frequency, the buzzer assembly can create audio sounds of different frequencies at comparable volume levels. The buzzer assembly preferably outputs a relatively consistent volume across the frequency range of 1-4 kHz, thereby covering two octaves. 
     An alternative embodiment does not move the buzzer, but rather changes the volume of air within the gasket through the use of a variable geometry deformable gasket. The deformable gasket may include one or more piezo-electric films that change shape in response to various electrical currents. By changing the internal shape of the buzzer gasket, but keeping the buzzer stationary, the buzzer assembly may still change its resonant frequency by changing the acoustic impedance seen by the buzzer. 
     Another alternative embodiment uses a gasket of a fixed size, but includes an extra chamber acoustically communicating with the interior of the gasket. The volume of this extra chamber is changed by means of a translational actuator attached to a piston within the extra chamber. The change in volume of the extra chamber likewise changes the resonant frequency of the buzzer assembly and allows different frequencies to be created by the buzzer assembly at comparable volume levels. 
     Yet another embodiment uses a conventional gasket, but changes the size of the chamber within the buzzer itself, thereby changing the resonant frequency of the buzzer assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a fragmented side view of the preferred embodiment of the present invention as seen in a communications device; 
     FIG. 2 depicts a top view of the device of FIG. 1; 
     FIG. 3 illustrates a cross-sectional view along lines  3 — 3  of FIG. 2; 
     FIG. 4 features a side view of a second embodiment of the present invention as seen in a fragmented communications device; 
     FIG. 5 pictures a top view of a third embodiment of the present invention as seen in a fragmented communications device; 
     FIG. 5A shows a top view of an alternative embodiment of FIG. 5 using a piezo-electric translational actuator. 
     FIG. 6 demonstrates a top view of a fourth embodiment of the present invention as seen in a fragmented communications device; and 
     FIG. 6A shows a top view of an alterntive embodiment of FIG. 6 using a piezo-electric translational actuator. 
     FIG. 7 shows a block diagram of the electrical control circuitry of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Turning now to the drawings, FIGS. 1-3 show one embodiment of a variable frequency buzzer assembly  10  of the present invention. The buzzer assembly  10  is positioned in a personal communications device  11 , which may be a cellular telephone, satellite telephone, personal communications assistant, pager, or similar device. For simplicity of description, a cellular telephone will be used as the illustrative personal communications device  11  for the balance of this description; but it is to be understood that the invention is not limited thereby. Cellular telephone  11  includes a generally surrounding frame  13  which includes a call alert aperture  12 . The call alert aperture  12  is typically proximate the antenna (not shown) and typically opens perpendicular to the plane of the phone&#39;s speaker (not shown) which conveys audio signals to the ear of the listener. 
     The buzzer assembly  10  includes a buzzer  20 , a translational actuator  22 , and a buzzer gasket  25 . The buzzer  20  may be any one of a variety of conventional buzzers known in the art, such as part number EAF8RM08ER, from Matsushita Electronic Components Co., Ltd. of Matshusaka Mie, Japan. Typical buzzers  20  are approximately half the size of a postage stamp and approximately 2 mm to 5 mm thick; as a result, typical buzzers  20  are extremely light. Buzzer  20  includes a buzzer aperture  27  which permits passage of noise emitted within buzzer  20  into air chamber  26  within expandable gasket  25 . 
     In a conventional cellular phone  11 , the buzzer  20  is rigidly attached to the frame  13  of the phone  11  with a foam gasket positioned between the buzzer aperture  27  and the call alert aperture  12 . During assembly, the gasket is attached at one end to the buzzer  20  by a conventional adhesive. When the frame  13  of the phone  11  is closed, the gasket is compressed to an initial degree, forming a seal with the buzzer  20  and the frame  13 , thereby insuring that there is a fixed volume of air between the diaphragm of the buzzer  20  and the call alert aperture  12 . 
     In contrast, the buzzer  20  of this embodiment is slidably positioned in guide track  21 . Guide track  21  preferably includes four guide rails  24  (best seen in FIG.  3 ), one on each side of generally rectilinear buzzer  20 . Translational actuator  22  moves buzzer  20  within guide track  21  by means of connector  23 . In the preferred embodiment translational actuator  22  is a conventional electric solenoid that is capable of variable positioning. For some alternate embodiments, the translational actuator  22  may be a piezo-electric film (not shown) disposed generally perpendicular to the direction of travel for the buzzer  20 . Since buzzer  20  is light weight, actuator  22  may be comparatively weak, thus keeping power requirements to a minimum and preventing undue power drain on the battery of the cellular phone  11 . 
     Expandable gasket  25  forms a tight seal between frame  13  of the phone  11  and the body  28  of the buzzer  20 . The seal need not be absolutely gas tight, but should be such as to significantly prevent the rapid flow of gas through the gasket, such that the gasket is effectively gas-tight for the changes in gas pressure expected in the typical acoustic range. Gasket  25  is preferably a closed cell foam gasket or an annular piece of preformed plastic with creases therein which expand and collapse like an accordion or bellows in response to the movement of buzzer  20 . The interior portion of the gasket  25 , between the frame  13  and the buzzer  20  forms a portion of air chamber  26 . Air chamber  26  also includes the chamber portion on the inside of the body  28  of the buzzer  20  with buzzer aperture  27  linking the two portions of the air chamber  26  in this embodiment. The portion of the frame  13  bounding air chamber  26  should include the call alert aperture  12 . In contrast to the conventional gasket described above, gasket  25  is initially compressed to a first degree during assembly, but then also further compresses and decompresses as the buzzer  20  slides within guide track  21 . Expandable gasket  25  changes shape, and thus changes the volume of air chamber  26 , in response to the translation of buzzer  20  within guide track  21 . 
     Air chamber  26  presents a specific acoustic loading to the sound generating diaphragm inside the body  28  of the buzzer  20 . The magnitude of the loading is partially a function of the volume of air in the air chamber  26 . This acoustic loading, or impedance, in turn determines the resonant frequency of the buzzer assembly  10 . By changing the volume of air chamber  26 , the acoustic impedance is changed, thereby creating a different resonant frequency of the buzzer assembly  10 . By operating the buzzer  20  at or near the resonant frequency corresponding to the current acoustic impedance, the buzzer assembly  10  can create audio sounds of different frequencies at comparable volume levels. 
     The mechanical action of the translational actuator  22 , and thus the acoustic impedance of air chamber  26 , is controlled by a suitable control circuit that coordinates the action of translational actuator  22  with the desired frequency to be produced by the buzzer  20  as described below. While the buzzer assembly  10  preferably outputs a relatively consistent volume across the frequency range of 1-4 kHz, thereby covering two octaves, the buzzer assembly  10  may provide a relatively consistent volume across the larger frequency range of 1-4.5 kHz. 
     An alternative embodiment of the buzzer assembly  10  is seen in FIG.  4 . In this embodiment the buzzer  20  is attached to deformable gasket  30  that changes shape without requiring the buzzer  20  to be displaced. This embodiment replaces gasket  25  with deformable gasket  30  that may include at least one piezo-electric film  31 , and preferably two films  31 , which deform upon application of electrical current thereto. Gasket  30  must still maintain an effective seal between buzzer aperture  27  and frame  13  of phone  11 ; thus, films  31  may be optionally contained within a closed cell foam gasket or the like. When films  31  deform upon application of current thereto, the volume within air chamber  26  changes to change the resonant frequency of buzzer  20  as discussed above. For purposes herein, the film(s)  31  are considered translational actuators. 
     Another embodiment of the buzzer assembly  10  is shown in FIG.  5 . In this embodiment, air chamber  26  is changed to further include a variable-sized second chamber  52  that helps regulate the acoustic impedance of air chamber  26  encountered by the buzzer  20 . This second chamber  52  is substantially external to gasket  50  as shown in FIG. 5, but is fluidly connected to the chamber formed by the interior of gasket  50  by neck  53 . The volume of air within second chamber  52  is varied by piston  54  driven by translational actuator  55 . Since gasket  50  should be gas tight, piston  54  should have a good seal with walls  56  of second chamber  52 . This may be accomplished with an o-ring (not shown) positioned around piston head  57  or other similar sealing means. Translational actuator  55  is preferably a solenoid, but may be a piezo-electric device  55   a  (see FIG. 5A ) hydraulic, pneumatic device, or similar device, which linearly drives piston  54 . Neck  53  may be of any suitable size, but preferably the neck  53  is not a quarter wavelength of any desired frequency to prevent the formation of standing waves therein. Alternatively, the neck  53  may be sized so as to resonate at the highest desired frequency when the second chamber  52  is at a minimum (e.g., piston  54  is fully extended). Movement of piston  54  within second chamber  52  changes the oscillating characteristics of the air in neck  53  and thus the resonant frequency of buzzer assembly  10 , in a fashion approximating a Helmholtz resonator. The air in the neck  53  will oscillate at a frequency dependant on the volumes at either end of the neck  53 . Thus, the oscillation in the neck  53  may be tuned by varying the volumes of the air chamber  26  and/or the second chamber  52 . 
     Another embodiment of buzzer assembly  10  is shown in FIG. 6, wherein air chamber  26  is defined by gasket  61  that is constant in size and variably sized chamber  62  in buzzer  60 . In this embodiment, translational actuator  63  drives piston  64 , which travels between stops  65  and  66 . Movement of piston  64  changes the volume of air in chamber  62  within the body of buzzer  60 , thereby creating different resonant frequencies for buzzer diaphragm  67  and coil  68 . Translational actuator  63  again may be a solenoid, piezo-electric device  63   a  (see FIG. 6A ) pneumatic, hydraulic or other similar device as desired, although a solenoid is preferred. 
     For proper functioning of the various embodiments of the buzzer assembly  10 , the translational actuators need to be controlled. A control circuit, such as that seen in FIG. 7, may be incorporated into cellular phone  11  for such purposes. The control circuit of FIG. 7 includes an audio alert controller  102  connected to phone controller  100 , translational actuator  104 , and preferably buzzer  103 . The phone controller  100  controls the overall operation of the phone  11  in a manner known in the art. The phone controller  100  may be of any type known in the art, such as a common microprocessor. Audio alert controller  102  controls the movement of translational actuator  104  so that movements of translational actuator  104  are synchronized to desired changes in ring frequency of buzzer  103 . While the audio alert controller  102  may be a portion of the phone controller  100 , the audio alert controller  102  is shown separate therefrom for illustrative purposes and preferably takes the form of a mixed signal ASIC chipset. Buzzer  103  may be buzzer  20  or buzzer  60 , depending on the embodiment and translational actuator  104  may be actuator  22 , piezo-electric films  31 , actuator  55  or actuator  63 , again depending on the embodiment. In the first embodiment, wherein buzzer  103  is buzzer  20  and moves, electrical connections to buzzer  20  are preferably short wires or flex film connections, which allow buzzer  20  to move on guide track  21  (FIGS.  1 - 3 ). As discussed in regards to the second described embodiment, films  31  are considered translational actuators because while integrated within gasket  30 , films  31  perform the physical movement through their deformation, which actuates the change in volume of the interior of gasket  30 . If, as in the second, third, and fourth described embodiments, the buzzer ( 20  or  60 ) remains stationary with respect to the frame  13  of the phone  11 , the buzzer  20 , 60  may be connected to the control circuit in any conventional fashion, such as by printed circuit board traces. 
     The audio alert controller  102 , activates the buzzer assembly  10  to generate an audio alert signal to the user. For instance, the alert controller  102  may receive a trigger signal from phone controller  100  when an incoming call is detected. Preferably, the phone controller  100  also notifies the audio alert controller  102  which may use a plurality of “alert sounds” stored in memory  110 . The audio alert controller  102  then retrieves sound generating information from memory  110 , and activates the buzzer  103  and the translational actuator  104 . The sound generating information preferably includes either movement instructions or frequency information from which movement instructions may be determined. The translational actuator  104  is then moved in such a fashion as to cause the buzzer assembly  10  to generate the desired alert sound. For instance, if the desired alert sound is a melody, the translational actuator  104  would be sequentially moved to the proper position for each note, so that the resonant frequency of the buzzer assembly  10  is adjusted to the frequency of that note for the appropriate time. Then the translational actuator  104  is moved to the position corresponding to the next note, and so forth. 
     By changing the resonant frequency of the buzzer assembly  10 , the volume of the output of the buzzer assembly  10  through the call alert aperture  12  may be held relatively constant across a variety of frequencies. 
     It should be noted that the various alert sounds stored in memory  110  may be predetermined by the phone&#39;s manufacturer, or the phone may allow the user to establish their own alert sounds by any method known in the art. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.