Abstract:
A portable electronic bar code reader having an improved mechanism for producing sounds. The mechanism includes two piezoelectric disks, each positioned in a separate Helmholtz resonator tuned to a predetermined acoustic frequency at which the piezoelectric disks resonate. The mechanism also includes electronic circuitry for exciting the two piezoelectric disks at the predetermined frequency. The Helmholtz resonators are placed within the bar code reader and drive separate sound channels that are connected to opposite laterally directed sides of the bar code reader. When the piezoelectric disks are driven in phase at the predetermined frequency, the acoustic energy emitted from the two Helmholtz resonator combines in phase in the place where the user is located.

Description:
TECHNICAL FIELD 
     This invention relates to a method and apparatus for producing a sound, and more particularly, for producing a sound directed toward a user from a source that is not pointed in the direction of the user. 
     BACKGROUND OF THE INVENTION 
     Handheld units are becoming an increasingly popular way of packaging portable electronic devices. Examples are cellular telephones, small tape recorders and bar code readers. With the advent of microelectronics, increasing computational power and more convenience features are being put in portable electronic devices. The increased computational power and greater number of convenience features generally results in an increased number of control functions in such electronic devices, and usually such control functions are realized by means of an array of buttons in a keypad, a visual readout of a display unit, and a confirming sound maker. 
     There is an obvious trade-off between the decreasing size of the portable electronic unit and the number of control functions it can perform. One place where this trade-off is most visible is in the amount of surface area that the portable electronic device presents to its user. Keypads with a given number of keys cannot be made smaller than a certain size without inconveniencing users with even average size fingers. The size of display units cannot be decreased beyond a certain point or they become unreadable by the user. Further, the size of a sound maker cannot be decreased beyond a certain point, or the fidelity and audibility is too badly degraded for user acceptance. Therefore, it is common for the entire front surface area of a portable electronic device to be used entirely to hold a keyboard, a display unit and a miniturized speaker, in order to avoid reducing the size of any one of these items below the size that would be acceptable by users. It would be advantageous to remove at least one of these items from the front side of device (without degrading its performance or the acceptability of the device to users). 
     Many of the portable electronic devices that are currently in use must be capable of operating in areas that have high sound levels. For example, bar code readers are commonly used in noisy production areas where it is hard for the user to hear any confirmatory sound signals generated by the device. Further, several such devices are also commonly used within a small work area, increasing the chance that the confirmatory signal from one such device will be misinterpreted as being a confirmatory signal from another such device. Therefore, it is desirable to have a portable electronic device that can produce highly intense sound signals that are primarily presented to the user (without requiring that the sound maker be positioned at the front side of the device). 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention is a sound-emitting handheld apparatus. The apparatus comprises a case, a sound-producing mechanism and at least one sound-conducting channel. The case has an exterior surface and is adapted to be held by a user with a preferred first portion of the exterior surface toward the user while the apparatus is being used. The sound-producing mechanism is located within the case. The at least one sound-conducting channel connects the sound-producing mechanism to a second portion of the exterior surface other than the preferred first portion of the exterior surface. 
     In another aspect, the invention is a method for producing a sound from a handheld apparatus. The method comprises the steps of (a) providing a case having an exterior surface adapted to be held by a user with a preferred first portion of the exterior surface toward the user while the apparatus is being used, (b) locating a sound-producing mechanism within the case, the sound-producing mechanism producing a sound when it receives a signal representing the sound, and (c) connecting a sound-conducting channel from the sound-producing mechanism to a second portion of the exterior surface other than the preferred first portion of the exterior surface. The method further comprises (d) producing a signal representing a sound, and (e) causing the signal representing the sound to be received by the sound-producing mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is an isometric view of a portable electronic bar code reader. 
     FIG. 1B is a to plan view of the portable electronic bar code reader shown in FIG. 1A. 
     FIG. 1C is a bottom plan view of the portable electronic bar code reader shown in FIG. 1A. 
     FIG. 1D is a view of front obverse side of the portable electronic bar code reader shown in FIG. 1A. 
     FIG. 1E is a right side elevational view of the portable electronic bar code reader shown in FIG. 1A. 
     FIG. 2 is an isometric view of the portable electronic bar code reader shown in FIG. 1A, with the keyboard rotated upwardly from the bar code reader body. 
     FIG. 3A is an isometric view of the top shell of the portable electronic bar code reader shown in FIG. 1A, shown from the reverse side. 
     FIG. 3B is an isometric exploded view of the top shell of the portable electronic bar code reader shown in FIG. 3A. 
     FIG. 4 is a cross-sectional view of a sound channel of the portable electronic bard code reader. 
     FIG. 5 is a cross-sectional view of a Helmholtz resonator known in the prior art. 
     FIG. 6 is a polar plot of the sound intensity produced by the sound-producing mechanism of the preferred embodiment of the invention, taken in a plane transverse to the vertical axis of the portable electronic bar code reader. 
     FIG. 7 is a schematic drawing of the electronic circuitry of a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1A is an isometric view of a portable electronic bar code reader 10. Other views of the bar code reader 10 are shown in FIGS. 1B-E. The bar code reader 10 includes a body 12 having an upper enclosure portion 14 and a lower enclosure portion 16. The body 12 is substantially symmetric about the vertical axis 17. The body 12 is designed to be held in one hand of the user, while the user&#39;s other hand is used to enter and manipulate data and commands through a keyboard 18 which includes a plurality of keys 20. In use, the upper portion 14 of the bar code reader 10 is generally facing the user. 
     Various results, including the results of the keyboard entries through the keyboard 18 are displayable on a display 22. Display 22 can be made from an LCD substrate and connected to conventional electronic driving circuitry. The upper portion 14 and lower portion 16 of the bar code reader 10 define an enclosure which contains the electronic circuitry that will be described subsequently. 
     FIG. 1B is a top plan view of the portable electronic bar code reader shown in FIG. 1A. The top part of the lower portion 16 includes a conventional electrical connector 30 which can be used to receive a plug from a bar code scanning device (not shown), such as a bar code wand or a laser scanner. The signals produced by the bar code scanning device are sent to the portable electronic bar code reader 10 through the connector 30 and, in some applications, signals produced by the portable electronic bar code reader 10 are sent to the bar code scanning device through the electrical connector 30. 
     FIG. 1E is a right side elevational view of the right side of the portable electronic bar code reader 10 shown in FIG. 1A. Between the keyboard 18 and the lower portion 14 is a first sound channel 32 which leads to the interior of the enclosure defined by the upper and lower portions 14 and 16. There is an identical second sound channel 33 (see FIG. 4) which is symmetrically placed on the left side of the portable electronic bar code reader 10. The structure of the first sound channel 32 will be described in detail subsequently. 
     FIG. 2 is an isometric view of the portable electronic bar code reader 10 shown in FIG. 1A, with the keyboard 18 rotated upwardly from the body of the bar code reader 10. The keyboard 18, which makes electrical contact with the electronic circuitry inside an enclosure of the portable bar code reader 10 through the electrical connector 36, is supported by a top panel 38 of the upper portion 14 which has a pair of circular gaps 40a and 40b formed therein. The gaps 40a and 40b are aligned with and communicate with the first sound channel 32 and the second sound channel 33 formed in the upper portion 14. 
     The panel 38 is removably attached to the lower portion 16. FIG. 3A is an isometric view of the bottom side of the panel 38, and FIG. 3B is an isometric exploded view of the bottom side of the panel 38 shown in FIG. 3A. The bottom side of the panel 38 includes two symmetrically-placed circular walls 42a and 42b which are adapted to respectively receive and hold piezoelectric disks 44a and 44b. They are respectively held in place by adhesive annuli 43a and 44b. The outer edges of the piezoelectric disks 44a and 44b are respectively in close alignment to the gaps 40a and 40b. 
     When the piezoelectric disks 44a and 44b are properly excited by an electrical current, they flex in characteristic modes which are dependent upon the frequency of the electrical current, the dimensions of the piezoelectric disks 44a and 44b, and the material from which the piezoelectric disks 44a and 44b are made. Some of the sound which is produced as a result of the flexure of the piezoelectric disks 44a and 44b escapes through the gaps 40a and 40b, to the user who is holding the portable electronic device 10. 
     The piezoelectric disks 44a and 44b are enclosed in Mylar envelopes 45a and 45b, which cover the portions of the piezoelectric disks 44a and 44b that are closest to the exterior of the portable electronic bar code reader 10. This will prevent the occurrence of electrostatic discharge (ESD) conducted by the piezoelectric disks 44a and 44b to the electronic circuitry in the portable electronic bar code reader 10. 
     FIG. 4 is a cross-sectional view showing one of the sound channels 32 or 33 of the portable electronic bar code reader 10 extending from one of the piezoelectric disks 44a or 44b to the corresponding gap 40a or 40b. As will be discussed subsequently, the cross-sectional size of the sound channel is an important factor in the design of the sound-making capabilities of the portable electronic bar code reader 10. 
     The design of the sound channels 32 and 33 and the sound enclosure defined by the circular walls 42a and 42b are determined by the features of the so-called Helmholtz resonator. FIG. 5 is a cross-sectional view of a typical Helmholtz resonator, as applied to a piezoelectric disk 47 of the type used in the portable electronic bar code reader 10 and the sound enclosure formed by the circular walls 42a and 42b. The volume enclosed between the piezoelectric disk 47 and the sound enclosure formed by a circular wall 48 has only one sound channel 50 connecting it to the ambient atmosphere. It has been determined that a volume enclosed in this manner resonates at an acoustic frequency that can be determined from the formula: ##EQU1## where c is the speed of sound, a is the effective radius of the sound channel 50, d is the diameter of the circular wall 48, h is the separation between the piezoelectric disk 47 and a top wall 52, in which the sound channel 50 is formed, t is the thickness of the top wall 52, and k is a constant with a value of 1.3. An important aspect of the invention is that the size of the volume in which the piezoelectric disks 44a and 44b are placed is chosen to resonate at the resonant frequency of the piezoelectric disks 44a and 44b. By proper choice of the dimensions of sound channel 46, the sound at the resonant frequency is carried to the outside of the body 12 of the portable electronic bar code reader 10 with very little loss of the sound energy provided by the piezoelectric disks 44a and 44b. 
     The placement of the two gaps 40a and 40b symmetrically about the sides of the body of the portable electronic bar code reader 10 causes the sound waves emitting from the gaps 40a and 40b to reinforce one another along a plane that is perpendicular to the upper face of the upper portion 14 and to the line between the gaps 40a and 40b. Therefore, the user, who is normally located along or near this plane, will hear the sound produced by the portable electronic bar code reader 10 at high levels that are not possible in other forms of portable electronic devices. Furthermore, other persons, who are not users, will not be located along this plane and, accordingly, will not receive the same levels of acoustic energy produced by the piezoelectric disks 44a and 44b. This will ensure that the sound signals produced by a given portable electronic bar code reader 10 will be best heard by the user, and not heard well or at all by non-users. 
     FIG. 6 is a polar plot of the sound intensity (measured in dB) produced by the sound-producing mechanism of the preferred embodiment of the invention, taken in a plane transverse to the vertical axis 17 of the portable electronic bar code reader (see FIG. 1A). From FIG. 6, it is apparent that the maximum intensity of the sound is in a direction normal to the upper face of the portable bar code reader 10. 
     FIG. 7 is a schematic drawing of the electronic circuitry of a preferred embodiment of the present invention. This circuitry is contained in the enclosure defined by the upper and lower enclosure portions 14 and 16 of the portable electronic bar code reader 10. The circuitry includes a conventionally programmed microprocessor 60 which operates in accordance with a program stored in a memory 62 and which retrieves and stores data in the memory 62. The microprocessor 60 is connected to a controller 64 and an application-specific integrated circuit (ASIC) 66. The ASIC 66 is under the control of signals from the microprocessor 60 and the controller 64 and transmitted through a line 67 to the ASIC 66. 
     The controller 64 produces sounds in a manner conventional for microprocessors used in personal computers (PC). These standard PC tones are passed to the ASIC 66 through the line 68. In addition, the keyboard 18 sends electrical signals through a line 70 to a keyboard controller 72. The keyboard controller 72 receives its electrical power from a battery 74. The keyboard controller 72 produces electrical signals that signify key clicks and low battery beeps. These signals are combined in an exclusive-OR gate 76 with audio signals from a modem (not shown) which may be electrically connected to the portable electronic bar code reader 10 through the connector 30 (see FIG. 1B), and then transmitted to the ASIC 66 through a line 78. 
     The ASIC 66 includes a beep duration control circuit 80, a control register 82, and a volume control circuit 84. The signals received from the line 67 by the beep duration control circuit 80 determine the length of each of the sounds that are controllably produced in accordance with signals from the ASIC 66. The beep duration control circuit 80 produces a duration signal that is ANDed with the standard PC tones on line 68, in an AND gate 86. The output of the AND gate 86 is combined with the output signal from the exclusive-OR gate 76 in an exclusive-OR gate 88. This signal, which combines all of the acoustic frequency signals produced by the portable electronic bar code reader 10, is sent to the volume control circuit 84, which adjusts the volume of the signal in accordance with signals received through the control register 82 from the microprocessor 60 and the controller 64. 
     The output of the volume control circuit 84 is two pulsed signals BEEP0 and BEEP1, which are received by an analog multiplexer 90. The multiplexer 90 also receives electrical power from a rectifying circuit 92, which rectifies the acoustic signals produced either by the controller 64 or the exclusive-OR gate 76. Accordingly, the multiplexer 90 produces no output signal unless there is an acoustic signal input to the ASIC 66, either through line 68 or line 78. The analog multiplexer 90 produces appropriately times and formed acoustic frequency signals that are used to excite the two piezoelectric disks 44a and 44b. The duration and frequency of the acoustic signals produced by the piezoelectric disks 44a and 44b are completely controllable by the microprocessor 60. In particular, the acoustic signals can be produced in phase to generate a maximum sound intensity to the user. The microprocessor 60 can be reprogrammed at any desired time by a user through the keyboard 18 connected to the keypad controller 72, in the conventional manner well-known to those who are skilled in programmed microprocessors and/or PCs. 
     Although preferred embodiments of the present invention have been described, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous arrangements, modifications, and substitutions of parts and elements without departing from the spirit of the invention. Accordingly, the invention is not limited except as by the appended claims.