Communications: electrical – Audible indication – Electronic
Reexamination Certificate
1999-05-14
2001-04-03
Swarthout, Brent A. (Department: 2736)
Communications: electrical
Audible indication
Electronic
C116S14200R, C331S173000, C340S384300, C340S384720
Reexamination Certificate
active
06211774
ABSTRACT:
DESCRIPTION
Background of the Invention
1. Technical Field
The present invention relates generally to the production of sound and more particularly to a device and a method which mimic the sound tone and sound intensity of an electromechanical horn.
2. Background
Electromechanical horns are currently employed for a wide range of uses, including for providing audible warning signals for machinery applications, particularly vehicular and mobile applications.
Electromechanical horns include a flexible diaphragm, typically formed of a metal, fixed at the outside edge to a frame, and a magnetic slug that is connected to the diaphragm. An electromagnetic coil encircles the magnetic slug. The electromagnetic coil is electrically connected to a power supply through a set of conductive contacts. When an electrical current is directed through the contacts and the electromagnetic coil, an electromagnetic field is created which opposes the field of the magnetic slug driving the magnetic slug in a first direction from its static position. The magnetic slug and the contacts are configured so that as the electromagnetic coil is energized, the movement of the magnetic slug relative to the electromagnetic coil repeatedly makes then breaks the set of conductive contacts, repeatedly defeating and reestablishing the electromagnetic field. The oscillation of the magnetic slug and the attached diaphragm produce an audible sound which is commonly directed through a horn.
A substantial amount of mechanical wear is associated with this method of producing an audible sound resulting in an operational life that is relatively short.
Beyl, Jr., U.S. Pat. No. 4,204,200 discloses an electronic horn for producing a broad spectrum frequency which includes at least two wave signal generating oscillating circuits adapted to provide square wave pulsed voltage output of a selected amplitude and different fixed frequencies. The electronic horn according to Beyl, Jr., also includes a mixing means to adaptively mix the instantaneous output signals of each signal generating oscillator to provide a stepwise varying output signal. An amplifier receives the mixed signals of the oscillator circuits, amplifies the signal and transmits the signal to a loudspeaker.
What is needed is a device that generates a complex signal using a single wave signal generator that mimics the sound and sound intensity of a multi-frequency tone of a conventional electromechanical horn. Such a device may eliminate the high wear associated with electromechanical contacts and the brittle metal diaphragm which are susceptible to a high failure rate.
What is also needed is a device that eliminates the electromagnetic interference associated with the operation of relatively large mechanical contacts as they open and close.
SUMMARY OF THE INVENTION
The electronic horn for mimicking a multi-frequency tone according to the present invention includes a wave signal generator for generating an input signal and a complex signal generator for generating a complex signal across a transducer to mimic the sound and sound intensity of an electromechanical horn. The complex signal generator is connected to the transducer. The wave signal generator may include a wave signal generating oscillating circuit for generating an input signal having a frequency (f
x
)
The complex signal generator produces a complex output signal which may derive from a plurality of product signals. Each product signal may be the product of the division of the input signal. The complex signal generator may include a digital counter which produces a plurality of product signals, each of the plurality of product signals being a product of the division of the input signal. The plurality of product signals may be produced by dividing and redividing the input signal by a first number or a sequence of numbers.
A full bridge motor driver circuit may be conductively connected to the complex signal generator, with the transducer conductively connected to the full bridge motor driver circuit for driving the transducer with the complex output signal. In one embodiment of the invention, the transducer is a closed basket loudspeaker.
The complex signal generator may also include a signal processor circuit. In one embodiment of the invention, the signal processor circuit acts as a digital delay and may be employed to subtract portions of the input signal.
In one embodiment of the invention, three product signals produced by a digital counter are utilized, each of the three product signals being a product of the division of the input signal. A first product signal is transmitted to a transducer. A second product signal and a third product signal are transmitted to the signal processor circuit, which in this embodiment of the invention, includes an arrangement of four NOR gates. A control signal is produced by the signal processor circuit and is used to control the full bridge motor driver circuit. The two signals coming into the full bridge motor driver circuit control the output waveform. The signal going into a phase control side controls the current direction through an array of switches (transistors) inside the chip. The control signal is input to an enable pin which controls the timing of a “dead period” sent to the transducer to create a second frequency.
The full bridge motor driver circuit may include an integrated motor driver chip employed typically for motion control of a DC permanent magnet motor. Integrated motor driver chips have been employed in various applications to control the position of a motor armature. In such applications, when current is run through the motor in one direction the motor armature spins clockwise. When the current flow is reversed, the motor armature spins counter clockwise. This is what is meant by motor control and this is what the integrated motor driver chip controls, the direction of current flow through a motor, or in this case a transducer.
In the present invention a transducer acts in a sense as a single pole motor and the integrated motor driver chip controls the position of the transducer diaphragm. By using an integrated motor driver chip to control the diaphragm position, the sound produced is controlled. The device is capable of producing sounds of an essentially infinite range where a microcontroller (computer) is utilized to create the control signals to this chip. Additionally, by using an integrated motor driver chip as part of the signal logic stream the total logic needed to produce the signal can be minimized.
In one embodiment of the invention, the motor driver chip has three inputs that can be dynamically controlled. In one embodiment of the invention, two of the three inputs are used. The first input controls the phase (direction of current flow through the transducer and the frequency of diaphragm movement), the second input controls whether or not there is current flow in the transducer (on or off). In theory by controlling these two inputs, any sound could be produced. The third input may be employed in a separate embodiment of the invention to control a motor braking function built into the chip. This function may be employed to control how hard the transducer diaphragm hits the end of its throw. By having it reach the end of its throw as the transducer speed slows down (soft stop) the amount of wear to the transducer cone material or diaphragm may be reduced.
The full bridge motor driver circuit may also include a current limiting circuit for limiting current through the loudspeaker to maintain a stable dB(A) output intensity level at differing input voltage levels. This objective may be achieved employing a pulse width modulated current limit circuit. The full bridge motor driver includes logic that switches the polarity of the current that is run through the transducer and an enable pin is used to subtract parts of the waveform. This creates the missing pulses in the waveform impressed on the transducer.
The electronic horn and method according to the present invention mimic the sound of and produce a sound intensity comparable to an
Electronic Controls Company
Holland Joseph W.
Swarthout Brent A.
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