Click for next page ( 398


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 397
EM Introduction I. Introduction It. Ergonomic Considerations in Pedal Design Pedals Design Considerations brake pedal T - Need fast and error-fr~ e activation (speed and safety). - Locate within comfort angles of body movement (comfort reach/or posture). - Design a proper pedal resistance for the pedal actuation (strength requirement). - Be sure to accommodate the Sth-percentile female to the 95th | percentile male as she wn in SAE J833 (accommodation). l accelerator pedal - Need continuous operations during driving a bus. Range of operation of the pedal should be comfortable (comfort reach/or posture). - Deliver actuating forces effectively (strength requirement). - Be sure to accommodate the 5th-percentile female to the 95th | percentile male as shc wn in SAE J833 (accommodation). l ig Five ergonomic principles for the pedal design 1. Comfort of lower body posture, 2. Proper pedal actuating force. 3. Fast foot movement (speed), 4. Accurate pedal activation (safely), and 5. Accommodation of various percentiles of two different anthropometric populations - 5 percentile female to 95th percentile male. E-]

OCR for page 397
E-: Introduction I-2. Importance of Ergonomic Pedal Design Inappropriately designed brake and accelerator pedals might: 1. Cause musculoskeletal problems. => Holding a ciriver's foot at an awkwarc! angle on the pedals tires the driver overall, not just the driver's foot or ankle (Woodson, ~ 98 ~ ). 2. Cause undesirable pedal activation errors. => A large number of incidents have been reported in which a driver inadvertently depresses the accelerator when intending to depress the brake. This unintended! acceleration incidents are not due to mechanical failure, but caused by foot placement errors/or insufficient height difference between the brake and accelerator pedals (Proctor and Van Zandt, ~ 994~. 3. Cause uncomfortable leg postures for small or large drivers to operate the pedals. 4. Need excessive leg or ankle forces for weak drivers to actuate the pedals. E-2

OCR for page 397
E-~: Literature Review Il. Literature Review I. An optimum location of the pedal fulcrum: Ayoub and Trombley (1967) - Usecl a generic treadle pedal - Measure : travel distances of the ball-of-foot Pedal Actuation ~ Results | Optimum Location of Mechanism Pedal Fulcrum constant angle The closer the fulcrum is to the heel, forward of the ankle actuation (12 deg.) | the farther the ball-of-fc ot travels. | constant distance The closer the fulcrum is to the heel, at the heel actuation (1.9 cm) | the smaller the ball-of-f lot travels. | 2. The speed and accuracy of discrete foot motions: Kroemer (1971) - Measures: speed and accuracy of foot motions After a short learning period, the subject could perform the task with considerable accuracy and with very short travel time (averaging about 0. ~ sec.). The results strongly suggest the speed and accuracy of foot movements can be attained with practice. The pedal locations within a foot comfort zone will not significantly affect the speed and accuracy of foot movement. E-3

OCR for page 397
E-TI: Literature Review 3. The prediction of foot movement time: Drury (l 975) - Studier! on coplanar foot movements - pedals are in the sane plane. - Developed an equation to predict foot movement time. - foot movement time = f (task difficulty) = f (foot movement distance, pedal size, and shoe sole width) Used a modified equation of Fitt9s law by Welford (l 9681. - Drury's index of task difficulty (ID) D = logy-+ 0.5] where A = movement amplitude (distance) to centerline of target W = pedal width S = shoe sole width - Reciprocal (back-and-forth) foot movement time (RMT) RMT = 0. ~ 874 + 0.0854 x ID - Single foot movement time (SMT) SMT= RMT/1.64 - For noncoplanar pedals, movement time can be double. => Drury's equations are useful for predicting the effects of varying the width of a pedal and/or the distance between pedals on movement time. 4. An optimum angle of foot pedals: Hertzberg and Burke ~ ~ 97 - Used an aircraft brake pedal - Measure: maximum pedal forces An optimum angle of between 25 and 35 degrees produced the highest forces. The optimum angle was verified by asking the subjects to rate their ankle comfort at each angle; 80 % of the subjects preferred the optimum angle. E-4

OCR for page 397
Em: Literature Review 5. Design guidelines of a brake pedal depending on seat height: Woodson (1981) Since many brake pedal controls require some amount of force, the geometric relationship between the operator's leg and foot and the position and angle of the pedal is an important consideration. - Depending on the height of the seat, foot pedals not only must be placed within reach, but they also must operate in a direction that is compatible with the force application vector. Design I A high-seat h ight I Amid-position I Alow-seathe ght Parameters | (43.2 cmab ve) | seat height | (30.5 cmbel w) 1 brake pedal I l l configuration ~\/ ~f em brake pedal | 20deg.orl ss l 15-30deg. 1 30.deg.orrrore angle l l | brake pedal | 89 N (20 lb) ~ tax. | 178 N (40 lb) Max. 1 623 N (140 lb) Max. forces force downward and a little equally forward and mainly forward in a application | bit forward in a | downward in a | reversed curvili: tear direction straight line reversed curvilinear pattern pattern E-5

OCR for page 397
E-ITI: Analysis of Pedal Design Parameters Ill. Analysis of Pedal Design Parameters ITI-~. Pedal Design Variables 1. Accelerator and brake pedals used in a driver's work station neec! to be analytically characterized for a systematic design. 2. The following 14 dimensional attributes are utilized to clefine the design variables of the pe(lals: (~) length, (2) width, (3) depth, (4) diameter, (5) thickness, (6) curvature, (7) shape, (~) angle, (9) adjustment range, (10) location, (11) travel distance, (12) resistance, (13) control/response (CR) ratio, and (14) material property (You et al., 1 9951. 3. 26 pedal design variables are identified (see the table on next page). 4. The design variables are classified into three groups according to the following design characteristics: (~) ergonomic design variables (ED), (2) mechanical design variables (MD), and (3) aesthetic design variables (AD). Summary of Pedal Design Variables Pedal Component No. of Design Variables No. of Ergonomic Design Variables pedal plate ~ ~ ~ ~ O pedal arm 5 O pedal mounting base LO 3 => The pedal plate is the main pedal component interfaced with a driver foot. E-6

OCR for page 397
E-~: Analysis of Pedal Design Parameters Taxonomy of Pedal Design Variables Pedal Design Variables pedal plate lengthpedal plate length width thickness shape angle ELF material pedal arm length width thickness shape material pedal length mounting width base thickness angle re;~:loe location material Code Classification PDl 1 ED PD2 ED PD3 MD PD4 ED PD5 ED PD6 ED PD7 ED PD8 ED Pug ED PDl0 ED PD11 ED PD12 MD PD 1 3 MD PD14 MD PD15 MD PD16 MD PD17 MD PD18 MD PD19 MD PD20 ED, MD PD2 1 ED PD22 ED PD23 MD PD24 MD PD25 MD PD26 MD pedal plate width pedal plate thickness pedal plate shape pedal plate horizontal angle from the floor pedal plate lateral angle from a vehicle center line P32 angle ranges horizontal distance of PPRPj from wo4 vertical distance of PPRP from WO lateral distance of PPRP from WO pedal plate material pedal arm length pedal arm width pedal arm thickness pedal arm shape pedal arm material pedal mounting base length pedal mounting base width pedal mounting base thickness pedal actuation angle pedal actuation force pedal recovery force ~. horizontal distance of PMBRP~from WO vertical distance of PMBRP from WO lateral distance of PMBRP from WO pedal mounting base material (Note) 1. Pedal Design; 2. P3 - Pedal Plate Pivot; 3. PPRP - Pedal Plate Reference Point, 4. WO - Workstation Origin (the point on the workstation platfor~n underneath a seat reference point of SAE 50%; 5. PMBRP - Pedal Mounting Base Reference Point. E-7

OCR for page 397
E-TIT: Analysis of Pecial Design Parameters Taxonomy of Pedal Design Variables Pedal 1 ~1 , ~1 ,~ Pedal Plate Pedal Arm Pedal Base ~ ~ ~ ~ .... Hi.. ~ ~ ~ ~ .. _engt 1 ~: Length Length Width . ~ . . .. I .. Width Width Thickness Thickness Thickness Shape Shape l~.,.,., Lo c.ation I . . ~.~.~ ~ , .,i ..~ .~. , I Hi. ... .. .. .... . . ... . . ... ... ~ ~ T ...... .. M;ateria'l:~.:: ~ . Wrangle .... . .... . . ~ : _ :: ::a i:: i: : i: : :::: : : . : ~.~-,~ ~es:lstance~. ~ . . ~ . : ~::~:~ I: ~ :~ -' :~ :::: Hi I: I: ~ ~ :~ ~ ~ JO .:,:: : : Location Material * The shaded boxes represent ergonomic pedal design variables. E-8

OCR for page 397
E-TIN: Analysis of Pedal Design Parameters Key Design Considerations Related to the Ergonomic Pedal Design Variables Be: related ergonomic design principle) Design Variables ~ Code ~Des gn Consideration Comfort Force Speed S afety . pedal plate length PDI pedalplatewiclth ~ PD2 pedal plate shape PD4 pedal plate horizontal PD5 angle from the floor pedal plate lateral angle PD6 from a vehicle center line P3 angle ranges PD7 horizontal distance of PA PPRP from WO vertical distance of PPRP Pug lateral distance of PPRP PD ~ O from WO pedal plate material PD! pedal actuation angle PD20 pedal actuation force PD21 pedal recovery force ~ PD22 ~= Accom mo clation E-9

OCR for page 397
E-~: Analysis of Pedal Design Parameters ITI-2. Standard Bus Driving Postures T. When establishing a standard driving posture, biomechanical (force), physiological (muscle strength), and anthropometric (range of motion of a body joint) characteristics of a human must be considered integratedly for comfortable posture and proper force application (You et al., 19954. 2. Postural angles has been used as an alternative method for quantifying the load on musculo-skeletal structures which leads the development of pain and discomfort in occupational work situations. The significant correlations between the body posture and load implies the postural angles can be used as an effective indicator of the development of musculo-skeletal injuries as well. Observation of postural angles requires less specialized knowledge and has an easier calibration procedure than electromyography used to directly record a physiological estimate of load on relevant muscles (Aaras and Westgaard, 1988~. . The comfort zones (see the table and figures on next page) are generally locater! in the middle between the extreme limits of limb movement, but modifications for vehicular seating are made to minimize the muscular load against gravity (Diffrient et al., 19814. 4. The angle of each body joint of the standard posture (see the table on next page) is determined on the basis of the comfort zones defined in ergonomic design sources (You et al., 1995~. The optimum knee angles for applying normal forces on pedals are ~ ~ 0 to 120 deg. (Diffrient et al., 198 I). The optimum angular relationship between the lower leg and the pedal surface should be approximately 90 deg. (SAE Il 100, 1994; Woodson, 1981~. The recommended seat pan angles to support comfortable upper leg postures are 5 to 25 degrees (Diffrient et al., ~ 98 ~ ). E-10

OCR for page 397
E-~: Analysis of Pedal Design Parameters Comfort ROMs and Standard Driving Postures of Lower Body (unit : deg.) . Joint Movement | Comfort ROM * I Standard ~ riving Posture l | | Static Posture Dynamic Posture hip - :xion(oc) I [95,120] 1 95 90 | hip at auction (it) | [-5, 20 ~ ~O 1 0 ~| | (for brake) (for accelerator) Rotation (leg twist) (X) | [-15,15] | 0 0 leg knee flexion (a) [95' 135] 115 120 (for idle pedal (for full pedal ~press) press) foot ~ankleflexion(sj I [85,l]0] | 90 110 l | | (idle pedal (for full pedal l | press) press) Abduction (is) | [0, 15] | 0 2 * ROM - Range of Motion E-11

OCR for page 397
E-TV: Pedal Design Synthesis e 8 ~ _ 53k i. Ed ~0 - T_1' ~ ' E ~ , Fed 1 ~ ASH ''1 ~ ~& o o ~ .* _ e! l ! 5 'ail Phi 1', 1 hi ~. ~ 8 _ ~ _ S. _ D., It ~ te n1 1 D' 1 e' 3 ;t al ~ e' I S .' ! . l Be g 8 Sit _e i 1 T ~ 8 5 t - . ~ | S ~ 8's ~ de E-34

OCR for page 397
E-IV: Pedal Design Synthesis The determination of an optimum hip joint height was further investigated by relating the pedal actuation constraint and heel allowance range. The ranges of the heel locations which satisfy the pedal actuation constraint (in this study, 20 deg. is assumed for complete pedal actuation) is plotted in the following chart using the kinematic simulation results. The heel movement range signifies a postural allowance in this context; the zero tree! movement range means that a heel point needs to be at a specific location for the pedal actuation requirement. By combining the comfort movement zone size and the postural allowance, an optimum hip joint height of each population can be suggested. In this example, the optimum heights are 38 cm for the SAE 05% female, 43 to 44cm for the SAE 50%, and 49 cm for the SAE 95% male. 5. 0 _ . , ~, . . . . . 4.0 3.0 2.0 1.0 rat.- , ~ SAE 05% SAE50% ' SAE95% . ._ : :[49] . . [43-44] : / If: ~ '.1 ~ ,$ | ~ t ~ _ _ _ OF _ 1 ~ , 1 ., IN , . 28 32 36 40 44 48 52 Hip Joint (Hpt) Height (unit: cm)

OCR for page 397
E-IV: Pedal Design Synthesis 5. ~ Simulation Results 5. ~ . ~ Optimum Hip Point Location Utilizing the concepts discussed above for the determination of an optimum hip point location of a population, the simulation results are summarized in the table below. It is identifiec3 that the optimum hip joint locations are clependent on the initial P3 point height, pedal actuation requirement, and anthropometric population. The P3 point height and pedal actuation requirement determine the driving postures and foot rotation angle requirement of a certain population (see section TV-! and EV-3~. Optimum hip point location = f (driving postures, foot rotation angle requirement) = f (P3 Pt height, pedal actuation constraint) P3pt Height Design Variables Population 1 . . 1 SAE05% F SAE50 % Range SAE95 % M 6.16 cm Hpt to Heel pt . Heel Pt to Ball-of 44.6 cm 50.0 cm 54.5 cm 9.9 cm 14.8 cm foot 16.9 cm ~ 9.0 cm 4.2 cm ~-Li :: .. .. ................................................................... :::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::::::::::::::: ,.,,. ~,., ,, ~.......... ......................................................................................................... ......................................................................... ................................................................... 9.0 cm Hpt to Heel pt 53.2cm 58.2 cm 63.2 cm lO.Ocm Heel Pt to Ball-of foot 13.3cm 15.6cm 7.9 cm 4.6 cm 1.57 cm Hpt to Heel pt 61.Icm E-36 66.Icm 70.9 cm 9.8 cm

OCR for page 397
E-IV: Pedal Design Synthesis 1HOC1Pt1{ Ball-oP 1 ll.lcm I lS.Scm 1 16.4cm I 5.Scm I agog I I I I I (Pll! OCR for page 397
E-IV: Pedal Design Synthesis 5.1.2 Optimum Seat Reference Point Location In order to provide the optimum hip joint locations with the SAE 05% female to SAE 95% mate, the seat needs to be adjusted sufficiently. The following table shows that the seat shoulc! have the horizontal adjustment of 17.0 cm ant! the vertical adjustment of 7.8 cm where initial P3 point height is 9.0 cm - the initial foot angle from the floor is 30 deg. Conversely, the optimum pedal location can be determined using the simulation results of SRP to P3 point of SAE 50% (86.6 cm with the initial P3 point height of 9.0 cm). seat adjustment ranges = f (variations of optimum hip point location, variations of hip pt to SRP) P3 pt Height 6.16 cm Design Variables Hpt Height Hpt to Seat Range SAE 05% F Population SAE 50 % SAE 95 % M 40.0 cm 45.0 cm 49.0 cm 6.4 cm 8.0 cm 9.6 cm 9.0 cm 3.2 cm Hpt to P3 pt Hpt to Buttock 59.4 cm 11.6 cm 9.0 cm 1 1.57 cm Hpt Height Hpt to Seat 38.0 cm 6.4 cm 66.9 cm 12.8 cm . ~cm~.~ :::::::::::::::::::::::::::::::::::::::::::::::::::: ................................................. 43.0 cm 8.0 cm 73.5 cm 141 cm 49.0 cm 9.6 cm 2 4 cm 11.0 cm 3.2 cm Hpt to P3 pt Hpt to Buttock 66.5 cm 11.6cm Hpt Height 33.0 cm E-38 73.8 cm 12.8 cm ........ ................ ..~..~ ~ --I- ........ 40.0 cm 81.1 cm 14.6 cm 2.4 cm 46.0 cm 13.0 cm

OCR for page 397
E-IV: Pedal Design Synthesis To Set ~ 6.4 cm ~ 8.0 cm ~ 9.6 cm ~3.2cm ' . " ' ' ""'"" ' ' ''' ' . ,.,. . .......... , . . ......... . ,. ., ,., ' ' '''''':"'"' ............................ ............................. .................................................................................................. .................................................. , ,. ,. Hptto P3 Pt ~ 72.2 cm ~ 79.9 cm ~87.3 cm ~15.1 cm Hptto Bu tock ~ 11.6 cm ~ 12.8 cm ~14.0 cm ~2.4 cm $ p - .................................. '''' ' ........................ ..... ................... ..................................... .............................. 6. Design Guidelines and Suggestions Design Variables | Design Suggestions brake | horizontal d: stance of BPRPt from WO' | 86.6 cm pedal ~ vertical Lists nce of BPRP from WO ~1 1.57 cm | lateral distal ce of BPRP from WO | 8.9 cm accelerator ~ horizontal d stance ofAPRP~ from WO ~86.6 cm pedal | vertical dish nce of APRP from WO ~9.0 cm lateral distance of APRP from WO 21.7 cm (Note) 1. BPRP - Brake Pedal Reference Point; 2. WO - Workstation Origin (the point on the workstation platform underneath a seat reference point of SAE 50%; 3. APRP - Accelerator Pedal Reference Point. E-39

OCR for page 397
E-IV: Pedal Design Synthesis IV-6. Pedal Plate Material (PDI 1) 1. Key Ergonomic Principles: Safety 2. Design Guidelines and Suggestions The pedal surface material should provide a driver's foot with sufficient friction to prevent an undesirable slip of the foot on the pedal. IV-7. Pedal Resistance (PD21 and PD22) . Key Ergonomic Principles: Force and Accommodation 2. Design Considerations The minimum resistance should be greater than the exerted force on the pedal by the weight of the leg alone. The pedal should return to its initial position when the driver release the pedal. This elastic resistance also reduces the possibility of undesirable activation caused by accidental contact with the pedal (Sanders and McCormick, 1993). - For ankle operated pedals in continuous use, such as an automobile accelerator' the maximum and minimum resistances should be less than those of leg operated pedals, such as a brake pedal (Van Cott and Kinkade, 1972). - Maximum pedal resistance should never exceed the maximum force exertable by the weakest operator (Van Cott and Kinkade, 1972~. For frequently but not continuously used leg-operated pedals, a force of about 30/O of the maximum exertable is reasonable (Van Cott and Kinkade, 1972). E-40

OCR for page 397
E-IV: Pedal Design Synthesis 3. Design Guidelines and Suggestions Design Variables | Design Guide lines | Design Suggestions brake pedal resistance | 1.232.6 N (52.3 lb) Ma>. (Diffrient et | 66.8 - 155.8 N (leg-operated pedal) al. ~ 1981) (15 - 35 lb) 2. 178 N (40 lb) Max. for a mid-position seat (Woodson, 1981) 3.35.6 - 267 N (8-60 lb) (Van Cott and Kinkade, 1972) accelerator pedal | 1.28.9-40N(6.5-9lb Optimum; 1 31.2-40N resistance 44.5 N (10 lb) Max.; (7 - 9 lb) (ankle-operated pedal) 26.7 N (6 lb) Min. (Diffrient et al.' 1981). 2. 17.8N(4lb)Min.; 28.9 - 40 N (6.5 - 9 lb) (Van Cott and Kinkade, 19721. E-41

OCR for page 397
E-IV: Pedal Design Synthesis References Aarast, A., and Westgaard, R. H. (1988), Postural Angles as an Indicator of Postural Load and Muscular Injury in Occupational Work Situations, Ergonomics, 31 (6), 915- 933. Ayoub, M. M., and Trombley, D. J. (1967), Experimental Determination of an Optimal Foot Pedal Design, Journal of Industrial Engineering, ~ 7, 550-559. Casey, S., and Rogers, S. (1987), The Case Against Coplanar Pedals in Automobiles? Human Factors, 29 (1), 83-86. Compton, T. (1994), Driver Workstation Upgrade on Metro Transit Buses, Seattle, WA, Municipality of Metropolitan Seattle. Davies, B. T., and Watts, I. M., Ir. (1970), Further Investigations of Movement Time Between Brake and Accelerator Pedals in Automobiles, Human Factors, 12 (6), 559-561. Diffrient, N., Tilley, A. R. and Harman, D. (1981) Human Scale 7/8/9, The MIT Press. Drury, C. (1975), Application of Fitt's Law to Foot-Pedal Design, Human Factors, 17, 368-373. Glass, S., and Suggs, C. (1977), Optimization of Vehicle-Brake Pedal Foot Travel Time, Applied Ergonomics, 8, 215-218. Hertzberg, H. T. E., and Burke, F. E. (1971), Foot Forces Exerted at Various Aircraft Brake-Pedal Angles, Human Factors, 13, 445-456. Kroemer. K. H. E. (1971), Foot Operation of Controls, Ergonomics, 14 (3), 333-361. Morrison, R., Swope, I., and Halcomb, C. (1986), Movement Tinge and Brake Pedal Placement, Human Factors, 28 (2), 241-246. Mortimer, R. G. (1974), Foot Brake Pedal Force Capability of Drivers, Ergonomics, 17 (41. Oborne, D. I. (1987), Ergonomics at Work, John Wiley & Sons Proctor, R. W., and Van Zandt, T. (1994), Human Factors in Simple and Compl:ex Systems, Allyn & Bacon. E-42

OCR for page 397
E-IV: Pedal Design Synthesis SAL (1994), 1994 SEE Handbook, vol. 3, Warrendale, PA, Society of Automotive Engineers Incorporated. Sanders, M. S. and McCormick, E. J. (l 993g, Human Factors in Engineering ancit Design 7th ea., New York, McGraw-Hill Book Company Schmidt, R. ~ ~ 989), Unintended Acceleration: A Contributions, Human Factors, 3 ~ (3), 345-364. I ~ Review of Human Factors Snyder, H. (1976), Braking Movement Time and Accelerator-Brake Separation, Human Factors, ~ 8, 201-204. Van Cott, H. P., and Kinkade, R. G. (1972), Human Engineering Guide to Equipment Design, Washington, DC: U.S. Government Printing Office. Woodson, W. E. (1981), Human Factors Design Handbook, New York, McGraw-Hill Book Company. You, H., Bucciaglia, I., Lowe, B., Gilmore, B. I., and Freivalds, A. (1995J, Bus Operator Workstation Evaluation and Design Guidelines: An Ergonomic Design Process for a Transit Bus Operator Transportation Institute. Workstation, PTT 9523, The E-43 Pennsylvania

OCR for page 397