Patent Application
20150257684
1. Field
This invention relates to hearing testing pumps. In particular, it pertains to a reversible electric motor driven pump with drive shaft employing pump controls operably associated with the electric motor to selectively control the start, stop, operating speed and rotation of the drive shaft in either a clockwise or counterclockwise direction to drive a rotating gear with lever structure configured to reciprocate when driven by the drive, shaft to selectively compress bellows and/or a piston forcing air through a tubing structure to create positive pressure entering art ear canal in one mode, and expand the bellows and/or a piston to withdraw air from the ear canal and create negative pressure therein in another mode.
2. State of the Art
Special hearing tests, namely Tympanometry, employ air pumps to change the pressure in the ear canal during hearing testing. These instruments vary the pressure in the ear canal with a pump, generate a pure tone, and then measure the eardrum responses to the sound tone at different pressures. This produces a series of data measuring how admittance of the reflected sound varies with pressure and is plotted as a tympanogram. Normally, the air pressure in the middle ear canal is the same as ambient pressure, and under normal conditions the air pressure in the middle ear is approximately the same as the ambient pressure since the Eustachian tube opens periodically to ventilate the middle ear to equalize pressure. The tympanograms of a normal person show normal mobility of the eardrum and the conduction hones forming a symmetrical bell shaped curve tympanogram. A skewed tympanogram curve may reveal fluid in the middle ear, perforation of the tympanic membrane, scarring of the tympanic membrane, lack of contact between the condition bones of the middle ear, or a tumor in the middle ear; see http://en.wikipedia.org/wiki/Tympanometry.
One of the key parts of these pressure changing hearing equipment systems is the pump. It should be small, low power, low noise, safe, and inexpensive.
Current tympanometers use linear piston or harmonic/bellow-style pumps. Both concepts typically use a step motor or DC motor driving a threaded bar and a nut to convert the rotational motion into a linear shift. The nut is usually mechanically coupled to a piston or bellows. When activated by the motor, this linear drive alternatively compresses the bellows or piston compressing air or stretches the bellows and retracts the piston to expand from the ear canal as shown in
Other pumps use different linear movers, such as belts, tooth belts or levers. These pumps also need a means to detect at least one special displacement position of the mover, typically achieved by one or more switches.
Another pump routinely used for hearing tests is the peristaltic pump, see http://en.wikipedia.org/wiki/Peristaltic pump shown in
Consequently, for tympanometer type testing, bellows, pistons, or tube pumps are used. These pumps should have low noise, be bi-directional, lightweight, small low power, safe, provide up to ±600 daPa of pressure. They also should preferably be low cost and easy to service.
Existing pumps have the following drawbacks:
a. Tube pumps age quickly, consume much power, are big and relatively expensive.
b. Bellows and harmonica piston pumps use linear drives, based on threaded control rods or similar constructions. These drives are relatively complex and cannot easily be constructed from off-the-shelf components. The linear drives tend to be bulky and need additional means to calibrate their position.
c. Stepper motors effectively have multiple “toothed” electromagnets arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external control circuit. To make the motor shaft turn, first, one electromagnet is given power, which magnetically attracts the gear's teeth. When the gear's teeth are aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when the next electromagnet is turned on and the first is turned off the gear rotates slightly to align with the next one, and from there the process is repeated. Each of those rotations is called a “step”, with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle. The disadvantage of stepper motors is that initial position calibration is needed for step-motor based constructions that use end-switches. Their stepped movement causes these motors tend to generate significant unwanted noise. Moreover, stepper motors need a hold current even when not stepping, thus consuming idle power.
There thus remains a need for an inexpensive, compact, low power, long living pump for tympanometry. The device described below provides such an invention.
A hearing pump comprising: a reversible electric motor with a shaft, pump controls operably associated with the motor to selectively control the operating speed and directional drive of the motor shaft in cither a clockwise or counterclockwise rotation. A rotating gear is associated with the shaft with lever structure adapted to reciprocate a bellows or harmonic pump back and forth to alternatively compress or expand air to provide positive or negative pressure in the connected ear canal.
A potentiometer senses the position of the harmonic pump piston or bellows displacement. The controlling circuit uses this signal to initialize the pomp at startup and to know when the maximum displacement is reached.
The potentiometer-based position control allows more sophisticated pump control by the electric motor, and makes the initial position calibration of step-motor based constructions that use end-switches obsolete. The first derivation of the position dpos/dt can also be used as a measure of rotating speed.
The pump can be operated in a wide range of speeds, especially if equipped with a tachometer generator or tachometer-less speed controlling circuit. This allows the pump to reset very quickly.
The pump cannot operate continuously. However, with added valves, it can return to a middle position and continue pumping with relatively short interruption. Typical time constants for off-the-shelf components are 0.5 seconds for such a cycle. It can therefore generate quasi-constant pressure by closing the output terminal with an additional valve, rewind the pump, and then continue pumping. Existing constructions are relatively slow in rewinding, while this new servo-based construction can resume pumping in less than a second.
The invention thus provides a rotationally driven harmonica or piston style pump controlled by an electric motor with a potentiometer sensing the displacement of a gear driven connecting rod or lateral extension lever activating a bellows or piston, which alters the pressure within the ear canal during testing to provide different pressure levels of up to ±600 daPa of pressure within the ear canal.
The linkage from the motor to a bellows may be configured as a rocker arm to provide non-linear compression and expansion of the bellows.
The hearing test pump preferably uses an off-the-shelf (RC-model) servo as driving the gearing and electric motor. For the bellows, a disposable harmonica-style pipette may be used as a replaceable pump element in a configuration allowing a user to periodically replace the same. A potentiometer is used as the position encoder. Such a potentiometer is already Included in commercially available servos used in RC-models. To improve motor startup torque and speed control a tachometer may be employed. Also a negative-impedance-circuit may be included to improve DC-motor startup torque and speed control without the need of a tachometer. Such a negative impedance circuit can compensate the DC resistance of the motor coils and therefore provide a significantly improved speed control.
The complete pump unit thus uses user exchangeable components, and is itself a user-exchangeable module.
The pump preferably is equipped with a vent that allows it to open to the ambiance. This allows the pump to initialize to a defined start position without any pressure being built up.
In one configuration, an additional second valve may be included to allow quasi-constant pressure by adding a quick “rebreathing-cycle” via the bellows or piston. During such a “rebreathing cycle”, the second valve would close the air duct to the ear. A first valve then opens the pump to the ambience. The pump drive returns back to a middle position, then the first valve closes and the second valve opens again, thus resuming operation.
In one embodiment, the pump is structured as a one-piece housing with a sealing ear tip similar to that shown in Heller et al., U.S. Pat. No. 4,688,582
The invention thus provides an inexpensive, compact, low power, long living pump for tympanometry.
An example of the present invention is shown in
During tympanometry, the loudspeaker 44 would be driven with a tone of typically 226 Hz, and the microphone 42 records the sound pressure of this tone in the ear canal. During the recording, the pump 20 would generate a varying pressure from typically −400 dPa to 400 dPa. The recorded sound pressure as a function of pump-generated air pressure would then be processed and plotted as the typanogram.
Typically, the controller unit 34 would consist of a digital, controller with AD and DA converters, amplifiers, motor drivers, interfaces and display (all not shown).
The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
