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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 398
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 399
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 400
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 401
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 402
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 403
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 404
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 405
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 406
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 407
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 430
E-TV: Pedal Design Synthesis
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E-34
OCR for page 431
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 432
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
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Representative terms from entire chapter:
pedal plate
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!
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
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
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
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
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
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
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