GB2388998A

GB2388998A - Actively reducing noise produced by dental equipment

Info

Publication number: GB2388998A
Application number: GB0311742A
Authority: GB
Inventors: David Charles Moss
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-05-23
Filing date: 2003-05-22
Publication date: 2003-11-26
Also published as: GB0211840D0; GB0311742D0

Abstract

A device for reducing or cancelling noise produced by dental equipment comprises a microphone 1, a processing unit and loudspeakers 9a, 9b. The microphone 1 captures the noise signal to be reduced and the processing unit generates an output signal in opposition thereto. The output signal is emitted by the loudspeakers 9a, 9b to reduce or cancel the noise. Two microphones may be used adjacent to the loudspeakers 9a, 9b and the captured noise signals processed independently with the resultant output signals emitted by the adjacent loudspeaker. The device may be fitted to a dentist's chair (fig.3) or to a dentist's examining lamp (fig.4), or to a pair of headphones (fig.5).

Description

NOISE REDUCTION DEVICE

The present invention relates to a noise reduction device for dental equipment and particularly to a device which actively generates a signal to reduce or cancel the effect of dental equipment noise.

5 Many people find visits to the dentist an unpleasant or traumatic experience.

This is particularly true if the patients are unfortunate enough to need their teeth drilled, for a filling or similar procedure. Some patients are known to find the noise generated by a dentists drill frightening and for most others it is at least highly irritating. 10 From the point of view of dentists and their staff, frequent exposure to loud noise with a peak frequency of skill can provide a serious health hazard. There is therefore a need to reduce the amount of noise generated by a dental drill.

Noise levels experienced by dentists and patients can be reduced by the use of ear plugs or similar devices. However, wearing ear plugs for any length of time can 15 be uncomfortable. Additionally there is the high cost of providing a sterile pair of ear plugs for every patient so as not to spread ear infections.

In some applications there has been success by processing a noise signal with an adaptive digital filter so as to generate a signal that is the anti-phase of the input noise signal which may then be entitled by a loud speaker to reduce or cancel the 20 original noise signal. Such technology has not previously been used on dental drills.

An object of the present invention is therefore to provide a device which in operation reduces or cancels the effect of noise generated by a dental drill.

According to the present invention there is provided a device adapted to reduce or cancel the effect of noise produced by dental equipment comprising:

( a microphone, for capturing a noise signal the effect of which to be reduced or cancelled; a processing unit, adapted to receive and analyse the noise signal and to generate a noise signal in opposition thereto; and 5 a loudspeaker adapted to receive the generated signal from the processing unit and to emit a corresponding noise signal to reduce or cancel the original noise signal. The noise reduction device is preferably adapted to reduce or cancel the effect the noise produced by items of dental equipment such as drills or tooth polishers.

10 Preferably for optimum performance the processing unit is a digital signal processing unit incorporating an adaptive digital filter.

To allow a digital signal processing unit to be used there may be provided an analogue to digital converter to convert analogue signals captured by the microphone to digital signals which may be processed by the processing unit.

15 To prevent aliasing during analogue to digital conversion a first low pass filter, with a cut off frequency of half or less than half of the sampling rate of the analogue to digital converter may be incorporated in between the microphone and the analogue to digital converter.

As noise is usually generated by a dental drill in operation in a range of 20 frequencies between Dc and I OkHz the cut off frequency of the first low pass filter is preferably lOkHz. Additionally and preferably the sampling rate of the analogue to digital converter is greater than 20kHz.

Preferably to ensure there is a clear signal for the processing unit to process, the signal output by the microphone is amplified before being filtered and converted to a digital form.

Preferably digital signals output by the processing unit are converted to 5 analogue signals by a digital to analogue converter before being emitted by the loud speaker. The remove high frequency components in the analogue signal output by the digital to analogue converter generated by the digital to analogue conversion process a second low pass filter may be provided. Preferably the second low pass filter has an 10 upper cut off frequency of I OkHz.

Preferably the analogue signal output by the digital to analogue converter is amplified in addition to being filtered by the second low pass filter. Preferably the gain of the amplification is preset. In an alternative embodiment the gain of the amplification may be controlled either by the processing unit or by a manual control if 1 5 desired.

The device may incorporate more than one loudspeaker. Preferably the device incorporates two loudspeakers, enabling each loudspeaker to be placed adjacent to the ears of a user of the device.

Each loudspeaker may emit the same noise signal or each loudspeaker may 20 emit a different noise signal.

Preferably embodiments of the device wherein the loudspeakers each emit a different noise signal incorporate two microphones. Preferably one microphone is located adjacent to each loudspeaker and most preferably the noise signal captured by

( each microphone is processed independently and the resulting noise signal is emitted by the loudspeaker adjacent to a particular microphone.

The independent processing may be carried out by two independent processing units or by a single processing unit capable of processing a pair of signals S independently and simultaneously.

Preferably the device is adapted such that at least a pair of speakers and at least one microphone may be built into or fitted to such items as a dentists examining chair, a dentists examining lamp or a pair of headphones.

The invention will now be described further by way of example only and with 10 reference to the accompanying drawings in which: Figure 1 is a block circuit diagram of a device for reducing or cancelling the effect of noise of a dental drill according to the invention; Figure 2a is a block circuit diagram of a modified embodiment of the device of Figure 1; 15 Figure 2b is a block circuit diagram of a modified embodiment of the device of Figure 1; Figure 3 shows how the invention is adapted to be fitted to a dentists examining chair; Figure 4 shows how the invention is adapted to be fitted to a dentists 20 examining lamp; and Figure 5 shows how the invention is adapted to be fitted to a pair of headphones. -

Referring to Figure 1, a microphone I is used to detect noise signals generated by the operation of dental equipment in operation, such as a dentists drill, the effect of which is to be reduced or cancelled.

The microphone I is a Sennheiser e835. Other makes and/or models of 5 microphone may however be substituted for this particular model if desired.

To ensure the signal captured by microphone l is sufficiently strong to be processed, it is amplified by an amplif er 2.

The pre-arnplified signal is then passed through an analogue low pass filter 3 and converted to a digital signal by an analogue to digital converter (ADC) 4. The 10 purpose of low pass filter 3 is to reject any frequencies above half the sampling rate of the ADC 4 and thereby avoid aliasing of the signal during analogue to digital ( conversion. Noise recordings of tooth drilling show that the noise generated typically has a frequency range between DC and I OkHz. Therefore to allow the system to capture all 15 the frequencies of interest. The ADC 4 used has a sampling rate of greater than 20kHz and the low pass filter 3 has a sharp cut off at above 1 OkHz.

The digital signal output from the ADC 4 is input to a processing unit 5. The processing unit 5 is a digital signal processing unit incorporating an adaptive digital filter. The processing unit 5 generates an output signal the frequency components of 20 which are substantially in anti- phase 7 to the frequency components of its input signal. The alogrithrns to carry out the signal processing are written in 'C' for ease of development however other programming languages can be used to create similar

( alogrithms. In particular, to boost performance of time critical stages of the process assembly language can be used.

The signal output by processing unit S is converted to an analogue signal by a digital to analogue converter (DAC) 6. The signal at this stage contains high 5 frequency components due to the sample and hold process and these are removed by a low pass filter 7. As only signals with a frequency between DC and I OkHz are input to the processing unit S. frequencies in the signal output by the DAC 6 of greater than I OkHz are definitely produced by the sample and hold process. To remove these high frequency components low pass filter 7 has a sharp cut off above I OkHz.

10 To perform the required effective cancelling or reduction of dental equipment noise, a loud speaker 9 is used to emit the anti-phase signal generated by the processing unit 5. Before the anti-phase signal reaches the loudspeaker 9 it is boosted by an amplifier 8. The gain of the amplifier 8 is preset at a particular level to ensure loudspeaker 9 emits the anti-phase signal at a power level which optimises effective 15 noise reduction.

It would also be possible in an alternative embodiment to use an amplifier with variable gain as the amplifier 8. In such a case the gain variation may be either under the control of the processing unit 5 or under manual control as desired, to try to optimise the effective noise reduction.

20 As the typical user of a noise reduction or cancelling device has two ears, practical embodiments of the device contain not one but two loudspeakers 9a, 9b. In use each loudspeaker is positioned adjacent to an ear of the user.

Two embodiments incorporating two loudspeakers 9a and 9b are shown in Figures 2a and 2b.

In the arrangement shown in Figure 2a the noise signal from a single microphone I is captured anti-phase signal has been boosted by amplifier 8, however, it is split and fed to both loudspeakers 9a, Db. The same signal is thereby output by both loudspeakers 9a, 9b. To achieve balanced effective noise reduction the anti 5 phase signal output is generated from a signal captured by the microphone I which is placed substantially equidistant to each loudspeaker 9a, 9b.

In the arrangement of Figure 2b a pair of microphones la, lb capture signals which are processed independently requiring a pair of processors 8a, 8b. If however, a processor 5 able to process two signals independently and simultaneously is 10 available that single processor 5 may be used in place of the pairs of processors 5a, 5b. As the signals are captured and processed independently the output anti-phase signals differ. To allow for optimum effective noise reduction the microphones I a, I b are placed adjacent to their respective speakers 9a, 9b.

15 In Figures 3, 4 and 5 three practical embodiments for arranging the microphones I and speakers 9a, 9b of the device within a dentists surgery to provide for effective noise reduction are shown.

Figure 3 shows how the device may be adapted to be fitted to a dentists examining chair 10 to provide effective noise reduction for a patient 11. In this 20 position the speakers of the device will also provide a lesser measure of effective noise reduction for a dentist 13 operating on the patient I 1.

The speakers 9a, 9b are positioned on the sides of the headrest of the dentists examining chair 10, adjacent to the ears of the patient 11. A microphone I is positioned on the top of the chair if the embodiment of Figure 2a is used. If however

( the embodiment of Figure 2b is used microphones la, lb are fitted to the chair 10 adjacent to their respective speakers Qa, 9b.

The other components of the device, for amplifying 2, 8, filtering 3, 7 converting 4, 6 and processing 5 the captured signal and the anti-phase signal are 5 fitted to the back of the chair 10. Alternatively the components may be provided fitted to any other convenient surface in the vicinity of the dentists chair. The loudspeakers 9a, 9b and the microphones 1 or la,]b are connected to the other components by audio cable.

Figure 4 shows the loudspeakers 9a, 9b and a microphone 1 fixed to a dentists 10 lamp 12. This embodiment of the device provides a measure of effective noise reduction for both a dentist 13 and a patient 11, the major worth of the reduction being felt by the dentists 13.

The device is shown using the embodiment of Figure 2a. If the embodiment of Figure 2b were to be used microphones I a, lb would be provided adjacent to their 15 respective loudspeakers 9a, 9b.

The other components 2-8 of the device are built into lamp 12. Alternatively they may be provided at the end of the lamp support arm 14 or any other convenient location, connected to loudspeakers 9a, 9b and microphone I or microphones I a, lb by audio cable.

20 Figure 5 shows loudspeakers 9a, 9b and microphone I adapted to be fitted on a pair of headphones IS to provide effective noise reduction or cancellation for the wearer. The headphones 15 are shown worn by a dentist 13 but may also be worn by another member of the dentists staff or by a patient 11 or by a friend/relative of the patient 11 who is within the surgery when the dentists drill is in use.

( If the embodiment of Figure 2b rather than Figure 2a is used microphone I is replaced by a pair of microphones I a, 1 b fitted adjacent to loudspeakers 9a, 9b.

The other components 2-8 of the device are provided within the housings of loudspeakers 9a, 9b or may alternatively be provided as a pocket or belt carried unit 5 attached to the loudspeakers 9a, 9b and the microphone I or microphones la, lb by audio cable.

It is of course to be understood that the invention is not to be restricted to the details of the above embodiments only which are described by way of example only.

For example the audio cable linking loudspeakers 9a, 9b and microphone I or 10 microphones la, lb to the processing components 2-8 may be replaced by a wireless transmission systems.

Claims

( CLAIMS

1. A device adapted to reduce or cancel the effect of noise produced by dental equipment comprising: a microphone, for capturing a noise signal the effect of which is to be reduced 5 or cancelled; a processing unit, adapted to receive and analyse the noise signal and to generate a noise signal in opposition thereto; and a loudspeaker adapted to receive the generated signal from the processing unit and to emit a corresponding noise signal to reduce or cancel the original noise 1 0 signal.

2. A device as claimed in claim 1 wherein the processing unit is a digital signal processing unit.

3. A device as claimed in claim 2 wherein the digital signal processing unit incorporates an adaptive digital filter.

15 4. A device as claimed in claim 2 or claim 3 wherein an analogue to digital converter is provided to convert analogue signals captured by the microphone to digital signals to be processed by the processing unit.

5. A device as claimed in claim 4 wherein a first low pass filter is provided between the microphone and the analogue to digital converter.

20 6. A device as claimed in claim 5 wherein the filter has a cut off frequency of half the sampling rate of the analogue to digital converter.

7. A device as claimed in claim 6 wherein the low pass filter has a cut off frequency of less than half the sampling rate of the analogue to digital converter.

8. A device as claimed in any of claim S to 8 wherein the cut off frequency of the first low pass filter is 10 kHz.

9. A device as claimed in any of claims 5 to 9 wherein the sampling rate of the analogue to digital converter is greater than 20 kHz.

5 10. A device as claimed in any preceding claim wherein an amplifier is provided to amplify the signal output by the microphone.

I 1. A device as claimed in any one of claims 2 to 10 wherein a digital to analogue converter is provided to convey digital signals output by the processing unit to analogue signals.

10 12. A device as claimed in claim 11 wherein a second low pass filter is provided to remove high frequency components in the analogue signal output by the digital to analogue converter.

13. A device as claimed in claim 12 wherein the second low pass filter has a cut off frequency of I OkHz.

15 14. A device as claimed in any of claims 11 to 13 wherein an amplifier is provided I to amplify the analogue signal output by the digital to analogue converter.

15. A device as claimed in claim 14 wherein the gain of the amplifier is preset.

16. A device as claimed in claim 15 wherein the gain of the amplifier is variable.

17. A device as claimed in any preceding claim incorporating two loud speakers.

20 18. A device as claimed in claim 17 wherein each loud speaker is placed adjacent to an ear of a user of the device.

19. A device as claimed in claim 18 wherein each loudspeaker emits the same noise signal.

( 20. A device as claimed in claim 19 wherein each loudspeaker emits a different noise signal.

21. A device as claimed in claim 20 wherein the device incorporates two microphones. 5 22. A device as clamed in claim 21 wherein one microphone is located adjacent to each loudspeaker.

23. A device as claimed in claim 22 wherein the noise signal captured by each microphone is processed independently and the resulting noise signal is emitted by the loudspeaker adjacent to a particular microphone.

10 24. A device as claimed in claim 23 wherein two independent processing units are provided to independently process the noise signal captured by each microphone. 25. A device as claimed in any of claims 17 to 24 wherein the device is a dentist's examining chair.

15 26. A device as claimed in claim 25 wherein the device is fitted to a dentist's exammng lamp.

27. A device as claimed in claim 26 wherein the device is fitted to a pair of headphones. 28. A device substantially as hereinbefore described with reference to and as 20 illustrated in the accompanying drawings.