现代人因工程课件：lecture 4-controls and data entry devices

1、Chapter four: controls and data entry devicescontrols Wheel pushbutton lever keyboard mice etcFunctions of controls The primary function of a control is to transmit control information to some device, mechanism, or system. Type of information: discrete and continuous the distinction between controls

2、 and displays is becoming more and more blurred with the advent of advanced technology.Generic types of controls One simple way to classify controls is based on the type of information they can most effectively transmit (discrete versus continuous) and force normally required to manipulate them (lar

3、ge versus small)Factors in control design The overall utility of the control can be greatly influenced by such factors as ease of identification,size,control-response ratio,resistance,lag,backlash,deadspace and location.Identification of controls The identification of controls is essentially a codin

4、g problem. The primary coding methods include:shape coding of controlstexture coding of controlssize coding of controlslocation coding of controlsoperational method of coding controlscolor coding of controlslabel coding of controls combination: unique combinations and redundant codesControl-response

5、 ratio We call the ratio of the movement of the control device to the movement of the system response the control-response ratio(C/R ratio) control-display ratio (C/D ratio)C/R ratios and control operation Gross-adjustment movement travel time fine-adjustment movement adjust time optimum C/R ratiosR

6、esistance in controls Control manipulation takes principally two forms: the amount of displacement of the control and the amount of force applied to the control. A pure displacement control would have virtually no resistance to movement, and the only type of feedback would be the amount of movement

7、of the body member-isotonic controls a pure force control and involves no displacement-isometric controlsType of resistance Elastic resistance: such resistance varies with the displacement of a control device. Static and coulomb friction:the resistance to initial movement, is maximum at the initiati

8、on of a movement but drops off sharply.Continues as a resistance to movement,but this friction force is not related to either velocity or displacement. Viscous damping: feels like moving a spoon through thick syrup. Inertia:the resistance to movement caused by the mass of the mechanism involved. It

9、varies in relation to acceleration. Combining resistancesEffects of various combinations of control resistance on tracking performanceType of control resistance presentconditionelasticViscousdampinginertiaTime on target1YesNoNo602YesYesNo523NoYesNo444NoNoNo415NoNoYes356NoYesYes357YesYesYes348yesnoye

10、s27Deadspace and backlash Deadspace in a control mechanism is the amount of control movement around the null position that results in no movement of the device being controlled. Backlash is the deadspace at any control position.Design of specific hand-operated controls-cranks and handwheelsA particu

11、lar design maybe optimum for one criterion but not for another. It is important that the aspect of human performance one wants to maximize be specified before design parameters are chosen.Cranks and handwheels Cranks and handwheels frequently are used as a means of applying force to perform various

12、types of functions, such as moving a carriage on a cutting tool or lifting objects. The effect of size and friction on the aspects (total work, mean minutes to quitting) of operator performance.-PP351Data entry devices Chord versus sequential keyboardsindividual characters are entered in a specific

13、sequence, there being a specific key or other device for every character.A single input unit (e.g., a number, letter, or word) requires the simultaneous activation of two or more keys.(stenotype machines,pianos, mail-sorting machine)Keyboard arrangement Alphabetic keyboards Qwerty versus Simplified

14、keyboards numeric keyboards two different arrangements of the numerals-calculator versus telephoneOther data entry technology Handwritten gestural data entrySpecial control devices Teleoperators speech-activated control eye-activated controlChapter five: noiseIntroduction:noise, in general, is annoy

15、ing sound that can inversely affect safety and performance.Two primary attributes: intensity and frequencyquestion: the unit of sound? Can we hear the sound of 0 dB?Basic sound terminology Noise and sound: sound is used to describe useful communication or pleasant sounds; noise is used to describe d

16、istracting or unwanted sound. Frequency: the range of sound frequencies audible by a normal human ear is about 20-20000 Hz. Sound pressure: is measured in Newtons per square meter. Decibel(dB):the decibel is defined as 20 times the logarithm of the ratio of a measured sound pressure to the reference

17、 pressure.(hearing threshold)Combination of noise sources Scale for combining decibelsDifference between two decibellevel to be added (dB)Amount to be added to the higherdecibel level to find the sum (dB)03.012.622.131.841.451.261.070.880.690.5100.4110.3120.2Example: assume that the following machin

18、es with given noise levels are operating together in a shop:machine1-80 dBmachine2-80 dBmachine3-87 dBmachine4-82 dBhow much is the overall noise level by machine1,2,3 and 4?EXERCISE:according to the principle of energy combination,niipp122Calculate the relationship between ippLandLSupposed 0lg20ppL

19、ipiPsychophysical indicesLoudness is a subjective or psychological experience related to both the intensity and the frequency of sound.Unit of loudness: phonthe sounds of different decibel levels with different frequencies compare with the reference sound (1000Hz pure tone),when the comparison sound

20、 is judged to be equal loudness to the reference sound, the decibel level of the reference sound is given to the comparison one as its loudness(phon). Equal-loudness curvessone: one sone is defined as the loudness of a 1000 Hz tone of 40 dB(that is 40 phon),i.e., 40 phons=1 sone. A sonud that is jud

21、ged to be twice as loud as the reference sound has a loudness of 2 sones.Equivalent sound level Approximate method statistical method TWAApproximate methodTTLniiieq12110lg1080Statistic table of sound levelN12345678Central soundlevel dB(A)80859095100105110115RangedB(a)7882 8387 8892 9397 98102 103107

22、 108112113117TI(min)T1T2T3T4T5T6T7T8Example: In a workstation, if a 91dB noise occurred for 4 hours, a 99 dB noise occurred for 3 hours, a 110 dB noise occurred for 1 hour, calculate equivalent sound level.statistical method60250dLLeq9010LLdExample: the distribution of sound level measured in a down

23、town is illustrated in the following table,calculate the equivalent sound level. Statistic table of sound levelCentral sound leveldB(A)707580859095100105%461817251578Noise and loss of hearinglEffects of noiseHearing lossDeafnessNerve deafnessConduction deafnesslMeasure hearing-audiometerNormal heari

24、ng and hearing loss Nonoccupational hearing lossPresbycusis is hearing loss due to the normal process of aging.Sociocusis refers to hearing loss due to nonoccupational noise sources, such as traffic,radio,etc P596 figure 18-3 Occupational hearing loss It is resulted from continuous exposure to a noi

25、sy working environment over time. Recover Permanent lossTemporary hearing loss from continuous noise Temporary threshold shift at 2 min(TTS2): any shift in threshold from preexposure levels Relationship with the sound level of the noiseeffective quiet(6065dB). TTS2 is proportional to the logarithm o

26、f the sound-pressure level It is proportional to the logarithm of exposure time The maximum threshold shift is produced not at the frequency of the exposure noise, but at frequencies well above it.(700 Hz=1000Hz) Permanent hearing loss from continuous noise 4000 Hz is the frequency to which the huma

27、n ear is most sensitive. Range: 30006000Hz Figure 18-4, pp598 Figure 18-5,pp598 Must we wait for 10 or 20 years to discover that a noisy environment is potentially harmful? It is widely accepted that the average TTS2 from 8-h exposure to noise in young, normal ears is similar in magnitude to the ave

28、rage permanent threshold shift found in workers after 10-20 years of exposure to the same levels of noise. lHearing loss from noncontinuous noiseCumulative effectlPhysiological effects of noiselEffects of noise on performanceNoise exposure limits Exposure to any sound level at or above 80 dBA causes

29、 the listener to incur a partial dose of noise. A partial dose is calculated for each specified sound-pressure level above 80 dBA as follows: (time actually spent at sound level)/(maximum permissible time at sound level)Noise exposure limits It is widely accepted that a worker can tolerate noise lev

30、els higher than the PEL for shorter periods of time. The PEL exposure duration)(285/ )90(hourinnPELduratioTLdiscussion Consider a worker who, during a workday, is exposed to the following noise levels: 95 dBA for 3.5 h 105dBA for 0.5h 85 dBA for 4.0h Is such exposure safety?Standard for assessing in

31、termittent noise exposureD: doseCi: time duration of exposure at noise level iTi: maximum PEL at noise level in: number of all noise levels observedThe total dose, D must not exceed 100%. Otherwise, appropriate corrective measures must be used to reduce the dose to acceptable level, i.e., to 100% or

32、 below. niiiTCD1100Noise dose converted to TWA1016.61 log/10090TWADExample: assume that a worker is exposed to the following noise levels during an 8-h work shift:8:00-9:30 95 dBA9:30-11:30 90 dBA11:30-13:00 75 dBA13:00-15:00 95 dBA15:00-16:00 90 dBAAssess the workers noise environment.Special noise

33、 Impulse noise: a sound with a rise time of not more than 35ms to peak intensity and a duration of not more than 500ms to the time when the level is 20 dB below the peak. Infrasonic noise: noise with frequencies below the audible range, typically less than 20 Hz. Ultrasonic noise: noise with frequen

34、cies above the audible range, typically greater than 20,000 Hz.The annoyance of noise Various measures of exposure to noise. Figure 18-6(p608) Measures of noise exposureOne measure has been related to annoyance and community action is day-night level (Ldn).Ldn is used by the Environmental Protection

35、 Agency to rate community exposure to noise.The day-night level is the equivalent sound level (Leq) for a 24-h period with a correction of 10 dB added to noise levels occurring in the nighttime(10 p.m to 7 a.m.)The annoyance of noise Annoyance and community responseA linear relationship between Ldn

36、and the percentage of people in the survey who were highly annoyed. Figure 18-7(p608)Table 18-7 lists corrections that are to be added to Ldn to obtain a normalized Ldn.The normalized Ldn is used to predict community reactions. (Table 18-8) Handling noise problems Measure the sound level of the situ

37、ation with a sound-level meter. (usually in dBA).Keep away from reflecting surfacesHold the meter at arms lengthIn the place where the distance is between near field and reverberant field (free field). Near field: a distance of about twice the greatest dimension of the machine being measured (or the

38、 wavelength of the lowest frequency sound being emitted, whichever is greater) Reverberant field: too far away from the machine, sound reflections from walls and other objects Free field: sound-pressure level readings should be made. Noise control Control at the source: decrease frequency & soun

39、d level Control along the pathHigh-frequency noise is more directional than low-frequency noise and is more easily contained and deflected by barriers.Acoustic material and rigid sealed enclosure are main means for high-frequency range. (figure 18-9, p613)Full enclosures are not necessary to reduce

40、high-frequency noise. A single wall, or barrier placed between the source and the receiver will deflect much of the noise.Low-frequency noise will not be reduced at all by this means, it can easily go over or around the barrier.Figure 18-11, p615Noise control Control at the receiver OSHA requires employers to make available hearing protection devices to