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作者:楊哲彰(2005-03-15);推薦:徐業良(2005-03-23)

「道道實業防音防護具性能測試機台設計製作」計畫書

1.     現況描述

道道實業股份有限公司(www.doris-ind.com,以下簡稱道道實業)成立於民國六十九年,目前為工業用防護用具的專業OEM/ODM製造商,主要產品如圖1所示,包括護目鏡、防音耳罩、焊接用面罩與光學透鏡,以及相關之射出成型塑膠製品等,以出口外銷為大宗。

1. 道道實業生產之工業用防護用具

道道實業生產之防音防護具在外銷前,需符合相關測試國際標準,主要包括防音防護具頭帶夾緊力測試、疲勞測試、密合度測試、以及聲衰減性能測試等項目。目前道道實業並無相關測試機台,所有測試均需送至國外,成本高、費時久,若得到的測試結果不符標準時需作設計改善,又無法立即測試得知改善成果。

元智大學機械系先前接受勞委會勞工安全衛生研究所委託研究計畫,對於防音防護具相關測試標準與測試機台研發有相當經驗,因此道道實業規劃委託元智大學機械系設計、製作一系列防音防護具性能測試機台。先前已設計製作完成防音防護具頭帶夾緊力測試機台(如圖2),並交由道道實業使用中。

2. 測試機台整體配置圖

本計畫中道道實業將繼續委託元智大學機械系設計製作防音防護具「頭帶疲勞測試」與「聲衰減性能測試」兩項機台,期能建立該公司自行檢測工具,提升產品開發效率,縮短開發時間。測試機台將依相關國際標準測試規範設計製作,但此測試結果僅供廠商自行檢測產品之用,並不具有上市商品檢測之效力。

本計畫完成後將提供道道實業防音防護具頭帶疲勞測試與聲衰減性能測試兩項測試機台各一具、測試機台設計原理及使用說明若干份、並提供安裝、測試、使用訓練等必要技術支援。

2.     改善工作內容

2.1 防音防護具頭帶疲勞測試機台

防音防護具頭帶疲勞測試機台依據澳洲∕紐西蘭標準AS/NZS STANDARD 1270:2002 ACOUSTICS- HEARING PROTECTORS(如附件1)設計製作,主要功用在於測試防音耳罩頭帶(headband)部份在反覆開闔狀況下是否會產生疲勞破壞。基本需求是設計一個機構來進行耳罩反覆開闔的動作,且有4個設計上所必須達到的要求:

(1)   在反覆開闔動作中左右耳罩間的最近距離為25mm,最遠距離為200mm

(2)   耳罩反覆開闔次數不得低於1000次。

(3)   耳罩反覆開闔的頻率為10~12次∕分鐘。

(4)   測試時需防止耳罩脫落。

除前述反覆開闔功能需求外,長時間使用(如每日開闔一萬次以上)的可靠度也是設計考慮重點。如附件所示,此項標準中提供如圖3之參考機構圖。此參考機構係採用一個轉速約12 rpm的減速馬達為動力源,配合與曲柄滑塊四連桿機構,將旋轉動作轉換成水平方向的反覆開闔動作。此設計機構較複雜,所需空間較大,機構可靠性也較難維持。

3. 曲柄滑塊四連桿機構設計

本計畫希望利用兩個步進馬達或RC伺服馬達帶動齒條,並且透過單晶片與程式控制,驅動左右兩耳罩同步做反覆開闔運動,如圖4所示。此設計概念可以省去複雜的連桿機構,只需將馬達動力經過齒條一次傳動後轉換成水平方向的往復推力,空間利用上也較為簡單,加上單晶片的計算及顯示功能,開闔位置控制較精確,且可提供一表頭,明確顯示測試進度(目前反覆次數)。道道實業並要求開闔時最大距離可依操作者調整,以符合不同市場之規範。

4. 雙馬達驅動設計

除了模擬開闔動作之外,本機台另一設計重點是耳罩的固定的方式,必須考慮到不同耳罩之尺寸差異,讓耳罩在模擬過程中不致於鬆脫掉落。圖5與圖6為固定耳罩機構的概念設計,採用機械式扣合方式夾緊耳罩,基座在下方,不至干涉頭帶,以彈簧扣及黑色海綿墊配合兩側螺栓夾緊耳罩護蓋,可適應不同耳罩護蓋尺寸。

   

5. 耳罩固定機構設計概念

6. 耳罩固定機構動作示意圖

2.2 防音防護具聲衰減性能測試機台

本研究計畫製作之防音防護具聲衰減性能測試機台,主要依照澳洲∕紐西蘭AS/NZS 1270:2002 Acoustics-Hearing protectors標準(如附件2)設計。然而AS/NZS 1270採用「主觀法(subjective method)」,即以真人測試(real-ear attenuation)之方式,必須由專業人員在專業實驗室中執行,且為避免實驗誤差,對受測者有諸多要求。因此本測試機台參考我國國家標準CNS8454(如附件3),採用「客觀法(objective method)」之測試方式設計,以「聲學試驗頭型(acoustic text fixture, ATF)」作為測試媒介,以量測出代表聲衰減性能之「插入損失(insertion loss)」。此測試結果與主觀法以真人測試之方式相較,並無法完全代表該防音防護具真實的聲衰減性能,但測試速度快、成本低,可由非專業人員執行,適合作為產品於開發設計階段品質檢測之用。然而本測試機台之音頻產生模組(包含粉紅信號產生器、濾波器以及功率放大器)及揚聲器等均要求符合AS/NZS 1270規範,仍然能利用作為主觀法測試之用。

測試機台安置的環境需為擴散音場(diffusion field),依據AS/NZS 1270,測試信號為粉紅噪音(pink noise),並以帶通濾波後輸出各個不同中心頻率的1/3八度頻帶,如表1所示,且能夠產生如表2所示之之動態範圍(dynamic range)。該密閉空間之均勻性(uniformity)、方向性(directionality)、迴響時間(reverberation time)AS/NZS 1270均有規範,可參閱本文附件2之說明,且背景噪音不得高於表3所示之規定值。依據表2測試信號頻率計算,此擴散音場空間長寬高尺寸之一必須大於5.4公尺,因此非本測試機台設計範圍。

1. 測試信號中心頻率

測試信號之中心頻率(Hz)

125

250

500

1000

2000

4000

8000

 

2. 測試信號之音壓範圍

中心頻率(Hz)

測試信號之音壓範圍(dB, re 20u Pa)

125

0 to 80

250

-10 to 75

500

-15 to 70

1000

-20 to 70

2000

-20 to 70

4000

-25 to 85

8000

-10 to 95

3. 測試環境可允許的最大背景噪音

中心頻率(Hz)

1/3八度音階頻帶音壓(dB)

63

25

80

21

100

18

125

14

160

11

200

9

250

6

315

4

400

3

500

2

630

1

800

1

1000

1

1250

1

1600

2

2000

2

2500

1

3150

-1

4000

-4

5000

-2

6300

3

8000

10

10000

20

機台主要架構如圖7所示,聲學試驗頭型與揚聲器安裝於同一底座,其中聲學試驗頭可由操作者依操作程序手動拆裝,微音器(麥克風)安置底座上,當裝上聲學試驗頭型時,麥克風位置會位於聲學試驗頭型兩開口的中點,為量測音壓的中心參考點(reference point)。如圖8所示,音頻產生模組包含粉紅信號產生器、濾波器以及功率放大器,放大後的信號連接至揚聲器。訊號處理單元採用PIC單晶片控制器,接收來自麥克風的音壓訊號,進行運算後將衰減值(插入損失)結果以矩陣LCD顯示字幕輸出,亦可連接至電腦端顯示。

依據CNS8454,測試機台操作程序規劃如下:

將耳罩置於聲學試驗頭型上,並確認耳護蓋以頭型之耳朵為中心,對稱地調整頭帶,使其剛好接觸到頭帶支撐處。首先將聲學試驗頭型移除,量測參考點上125Hz250Hz500Hz1000Hz2000Hz4000Hz8000Hz之音壓值。接著將戴上待測耳罩的聲學試驗頭型安裝回底座上定位後30秒,再次量測所有頻帶之音壓位準,此時麥克風擷取的音壓為衰減後的音壓值,120秒後停止讀取,單晶片控制器計算此120秒內的音壓平均值後,與衰減前的音壓相減,差值即為插入損失。試驗程序至少重複三次,直至所有八音階頻帶之插入損失連續二次平均值的差值小於1dB

7. 防音防護具聲衰減測試機台系統架構圖

8. 聲學試驗頭型中心參考點示意圖

附件1AS/NZS STANDARD 1270:2002 ACOUSTICS- HEARING PROTECTORS

3.2.7 Headband flexing

A flexing device shall be used that generates a movement between two plates. An example is show in Figure 3.4.

The cups/headband shall be set to the mid-point of the range of their adjustment. If the cups/headband setting tends to change, the adjusted position shall be secured, for example, by means of adhesive tape. Such means shall not interfere with the normal pivoting of the cups on the headband.

Place the earmuffs onto the apparatus and secure the cups to the plates in an appropriate way, for example using elastic bands.

NOTE: For helmet mounted earmuffs it may be necessary to support the helmet shall.

Adjust the minimum separation of the plates to correspond with the face state separation of the earmuff cushions, or to 25 mm, whichever is the greater.

Adjust the maximum separation of the plates to 200 ±5 mm.

Cycle the earmuffs between the minimum and maximum separations for 1000 cycles at a rate of 10 to 12 cycles per minute.

NOTE: Ensure that throughout the test no part of the headband touches any object that will interfere with its mechanical action.

FIGURE 3.4 HEADBAND FLEXING MACHINE

LEGEND:

1= Base

2= Fixed mounting arms

3 = Fixed mounting platform

4 = Earcup clamps (only one show)

5 = Rocking arms, with parallel motion

6= Moving platform

7 = Locating bracket for free earcup

8 = Motor with reduction gearbox (position adjustable on base)

9 = Crank on slow speed shaft

10 = Connecting rod (adjustable)

11 = Counter

NOTE:

1.      For ear-muffs with restricted cup articulation, it may be necessary to bring the moving platform at its lower edge.

2.      This diagram is not to scale and should not be used as an engineering drawing for the construction of a headband flexing machine.

 

附件2AS/NZS STANDARD 1270:2002 ACOUSTICS- HEARING PROTECTORS

4.2.2.1.2 Uniformity

For each test signal, with the subject and subject’s chair absent, the sound pressure level measured with an omnidirectional microphone at positions 15 cm from the reference point on the front-back, right-left and up-down axes, shall not deviate by more than ±2.5 dB from the sound pressure level at the reference point. The difference between the right-left positions shall not exceed 3 dB. The orientation of the microphone shall be kept the same at each position.

4.2.2.1.3 Directionality

The directionality of the sound field shall be evaluated at the reference point for test bands with centre frequencies greater than or equal to 500 Hz, with the subject and the subject’s chair absent. The measurements shall be conducted with a directional microphone that exhibits in its free-field polar response at the one-third octave test bands, at least 10 dB front-to-side rejection for a cosine microphone, or at least 10 dB front-to-back rejection for a cardioid microphone.

The sound field shall be considered acceptable if, when the microphone is rotated about thereference point through 360 degrees in each of the three perpendicular planes of the room, the observed sound pressure level in each test band in each plane remains within the variation allowed in Table 4.2. The sound pressure levels may also be obtained by measuring at fixed 15-degree increments as the microphone is rotated 360 degrees in each plane.

Table 4.2

Allowable variation of sound-field sound pressure levels within each plane

Microphone free-field rejection, dB

Allowable variation, dB*

>25

6

20

5

15

4

10

3

<10

microphone not suitable

*For directional microphones whose free-field rejection values fall between the tabled values, compute the allowable variation by linear interpolation.

NOTE: The variation in microphone response as the microphone is rotated in a random-incidence field is related to the directional characteristics of the microphone and the degree of randomness of the field being measured. Thus allowable sound field response variations are related to the free-field directional response characteristics of the microphone. The microphone characteristics may be obtained by measurement in a free field or from the microphone manyfacturer.

4.2.2.2 Reverberation time

For each test signal, with the subject and subject’s chair absent, the reverberation time at the reference point shall not exceed 1.6 seconds.

附件3AS/NZS 1270 Appendix A: Calculation of SLC80 and Class of Hearing Protector

Appendix A4: Determination of class

Table A4 Specified SLC80 for Determination of Class

X (class)

Y (dB)

Specified SLC80 dB

1

90

10~13

2

95

14~17

3

100

18~21

4

105

22~25

5

110

26 or greater