Click for next page ( 12


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 11
CHAPTER 2. WORK STATION DESIGN 2.~ Design Concept The general objectives of the design methodology are to develop a work station which will accommodate the population extremes with minimum mechanical adjustment. Priority was given to design concepts which do not degrade safety. For example, the operator should be able to keep his or her feet firmly planted on the pedals and due to safety the pedal mounting points should be fixed to the bus. Previous approaches such as Carrier et al. (1992) suggested a movable pedal to accommodate operators of different height. This type of adjustment was discarded due to safety concerns. Other objectives include: visibility, reach, comfort, and adjustability. This study has suggested novel design concepts on the work station components of transit buses such as steering wheel, pedals, instrument panels to resolve the problems described by the operators in the survey and discussed by other researchers. In parallel, a systematic design approach was developed in order to analytically determine the positions, orientations, and adjustment ranges of the components, which will be discussed in the following section. The steering wheel control was designed regarding its orientation, size, and adjustment mechanism. Regarding the wheel orientation, Carrier et al. (1992) pointed out that the steering wheel should be more vertical than what is commonly used. This has two advantages: the ranges of motion of the body parts (back, shoulder, elbow, and wrist) related to steering wheel maneuvering are decreased for the typical operator and therefore his or her fatigue level would be reduced, and the 5th percentile female would be able to operate the steering wheel in a more appropriate and biomechanically efficient manner. - 2.]

OCR for page 11
As for the wheel size, a larger horizontal steering wheel whose diameter ranges from 508 to 559 mm causes many operators to reach forward and therefore to loosen the contact and support between the torso and the seat back. SAE J1100 recommends a steering wheel diameter of 450 to 560 mm for Class B vehicles. The wheel diameter was determined to a size (457 mm in this study) within the recommended range with which the operators can maintain comfortable steering maneuvering postures. Lastly, in order for the steering wheel to accommodate all of the positions and orientations required to provide sufficient visibility and comfortable reach for the small and large operators, the wheel must have three degrees of freedom: a hub orientation adjustment, a column telescope adjustment, and a column tilt adjustment at the base of the steering column. Since an existing steering wheel system provides two degrees of freedom such as the hub tilt and the telescope, only a column tilt adjustment was added to the wheel assembly. The selection of pedal style is critical in the pedal design. Presently, the majority of transit buses use treadle pedals with an orientation angle between 40 and 50 degrees (Diffrient et al., 1981). The treadle pedal allows for little variability in placing the operator heel assuming the heel must be at the base of the treadle pedal for an efficient and safe pedal activation. Also, for most small operators, the extremely steep orientation of the accelerator results in an uncomfortable lower leg posture, which can cause unnatural extension or rotation about an ankle. In order to resolve the problems resulted from using treadle pedals, a hanging pedal was employed and evaluated in this study. The hanging pedal allows the operators to place the heel at more various locations on the work station platform than the treadle pedal. The orientations, activation angles, locations of accelerator and brake pedals with a hanging pedal style were determined based on comfortable reach of the right legs utilizing a kinematic model developed in this study, which is discussed in detail in Appendix E. The instrument panels containing displays and controls were investigated designing the adjustment range, panel layout, size, and locations (Appendix F). All instrument panels are adjustable to accommodate the population extremes in visibility - 2.2

OCR for page 11
and comfortable reach. The displays and controls are grouped according to their functional characteristics and systematically arranged into three areas: the left, central and right instrument panels. The functional purpose of the left instrument panel is to provide easy access for all operators to the secondary controls or controls that are used during the predriving tasks. These controls are the parking brake, the exterior mirror remote adjustment knobs, the exterior mirror defrost control, the internal and external public announcement systems, the radio controls, the run selector knob, the transmission and the ignition switch. The size of the left instrument panel is determined by the space required for the controls and the instrument panel is located in the side and plan views based upon comfortable reach of the left arms. The central instrument panel is intended to provide the operator with the operating status of the bus. Any information that does not require continuous monitoring by a particular gauge is replaced with an indicator light. To accommodate tell-tale indicators without giving up 0.95 cm by 1.27 cm of space for each of those indicators, it is proposed that the central instrumental panel have a small screen which can provide any of these tell-tales with the colors and required alarms. Since time is a large concern for operators and a significant part of their duties, a clock is also provided. The two most regularly monitored items on the central instrument panel are the speedometer and air pressure gauge. For this reason, traditional large dial readouts are provided. The intention of mounting the instrument panel directly on the steering column is that downward visibility will be improved. The purpose of the right instrument panel is to locate primary controls for driving and passenger pickup and depositing in an accessible and easy manner for all operators. The right instrument panel will contain a keypad with a small display called an operator digital assistant (ODA). The functions that can be accomplished through the digital assistant include: present the bus route schedule, control the farebox, perform automatic counting and categorization of the fares if used in conjunction with a card reading farebox or manually inventorying of the passengers when using a traditional farebox, print - 2.3

OCR for page 11
transfer tickets, monitor the gas mileage, change the destination sign, and in the future, possibly link with a global positioning system (GPS) for real time location of buses, and planning of proper routing to avoid delays. The data collected by this digital assistant can be easily downloaded at the end of the work day to a "home base" computer for analysis. The dimensions of the right instrument panel are based on the controls that it will contain. Also, comfortable reach of the right arms are considered in the determination of the right instrument panel location. - 2.4

OCR for page 11
2.2 Ergonomic Design Process The complexity of a bus operator workstation requires a systematic, welI-defined set of procedures, i.e., a systems approach, throughout workstation development stages. The techniques and analysis methods of a systems approach should be effective for a designer to define a complex system analytically, to identify crucial problems quantitatively, to manifest a design mechanism integratedly, and to suggest design guidelines rationally. A systematic design structure was constructed for the ergonomic bus operator workstation development in order to consider relevant ergonomic knowledge, design principles, and practices from contributing disciplines in an integrated way. The systematic design structure shown in Figure 2.! consists of four stages: (~) identification of design scope, (2) relationship analysis of design and anthropometric variables, (3) development of functional design relationship, and (4) synthesis of design guideline. 2.2.1 Design Scope Identification The design scope of a bus operator workstation was identified by choosing a design datum point, setting design criteria focused on the workstation design, defining static and dynamic bus driving postures, and establishing hierarchies of design and anthropometric variables. 2.2.~.1 Workstation Design Approach Three common datum points for ergonomic design have been applied to vehicle workstation design: (~) design eye position (DEP) approach, (2) heel reference point (HRP) approach, and (3) neutral seat reference point (NSRP) approach. In the DEP - 2.5

OCR for page 11
;h | Identify D. sign Scope | 1 Hierarchy of Design Var. Design Approach [D] (Datum Point) . , - Entity Design Criteria | - Attribute ~ - Modifier | Driving Posture | 1 ' 1 1 - 1 Hierarchy of Anthropometric Var. [A] - Entity - Attribute - Modifier Classify the Variables by Relationship Analysis 1 1 [D] x [A] ) Master / Precedence Cause / Relative Influence / Slave Effect Dependence . - ~ . Identify Design Niche Area & Functional Den ign Relationship 1 1 1 ._ Literature Survey - Design Guideline - Design Standard - Journal/Elandbook/ Technical Report - Data Base -~ ~ Imposture CD/3D CAM ~ CTask Analysis: ~ Posture Analysis ~ ~ ~iscomfort/Caus~ ~ CPreference:) ~ Field Survey - Questionnaire - Mockup Test - Prototype Test Suggest Design Guidelines Figure 2. I: Systematic Design Structure for an Ergonomic Bus Operator Workstation - 2.6

OCR for page 11
approach (Figure 2.2), the workstat~or~ design starts by setting the eye point which satisfies required visual fields along the sight line. Once the eye position is chosen, other design variables of the workstation such as the seat height and seat hack rest angle, and so on, are determined consecutively. Although this DEP approach results in good visibility, large adjustments for the seat and pedals are required to accommodate 95% of the U.S. adult population. This DEP approach is utilized primarily to design the space envelope for aircraft cockpits (Diffrient et al. ~981~. I'd Minimum Visibility Marker - Figure 2.2: Extreme Component Adjustments Required in the DEP Approac~ In contrast to the DEP approach, the HRP approach (Figure 2.3) begins by assuming that the various size operators have a common accelerator heel point (AHP). This HRP approach is applied mainly to industrial cabs such as tractors and lift trucks which require the highest possible seating to enable the operator to see down or up when bending forward (Diffrient et al., 1981). The benefit of the HRP approach is that almost - 2.7

OCR for page 11
no pedal adjustment is required, but relatively large adjustments for the seat and steering wheel are requires! to achieve the visibility requirement. A._._._ .~._.__ Cal L ~ '.. \ i Minimum Visibility Marker Figure 2.3: Visibility Cones Resulting from the HRP Approach The NSRP approach (Figure 2.4), which is employed in this study, encompasses the advantages from both the DEP and HRP approaches, with minimal component adjustments of the seat, steering wheel, and pedals. The SRP is defined as a point on the sagittal or medial plane of the seat located by the intersection of two planes: the compressed seat pan and seat-back. The SRP can easily be represented by either the hip pivot point (H-point) or seat index point (SIP) (Diffrient et al., 198 11. However, the SRP is not easily determined because the compressed planes are imaginary (Diffrient et al., 19811. Thus, auto makers have preferred to use the seating reference point (SgRP), which is the H-point (hip pivot point) of the 95th percentile person of the U.S. population (SAL I! 1001. According to SAE IS26 and SAE I! 100, the

OCR for page 11
SRP is located 13.4 cm behind and 9.8 cm below of the H-point which correspond to the profile of the deflected seating contour of the H-point machine as shown by Figure 2.5. Minimum Visibility Marker Figure 2.4: Visibility and Reachability in the NSRP Approach \~\ ~ ~J Figure 2.5: Geometric Relationship between H-point (SgRP) and SRP - 2.9

OCR for page 11
The SgRP position is determined by the following two analytical equations (Eq. 1 and Eq. 2) which incorporates the geometric relationship between the H-point and SRP, the seat pan angle, and the seat-back angle. horizontal distance of SgRP from SRP = HL12 - HL11 x cos(SB11) (1) vertical distance of SgRP from SRP = HLl ~ + HLl 2 x sin(SP9) (2) where, SB ~ i: seat back neutral vertical angle SP9: seat pan neutral horizontal angle HL`1 1: vertical length from hip pivot to SRP HLl2: horizontal length from hip pivot to SRP As an example, utilizing the equations and referencing the SgRP location specified in a seat drawing in Figure 2.6, the SRP of the seat is analytically positioned as of 1 1.7 cm behind and 10.7 cm below of the SgRP. in' Figure 2.6: Illustration Example of Locating SRP position from SgRP - 2.10

OCR for page 11
The NSRP design approach is accomplished by achieving a compromise between visibility and reach in the workstation design. Typically this approach requires a floor adjustment to support a heel point for comfortable pedal operation. In this study, however, only the pedal adjustment is considered without the floor adjustment for ingress/egress and safety reasons. 2.2.~.2 Design Criteria Design criteria for the workstation were based on four ergonomic principles: (~) visibility, (2) reach, (3) comfort, and (4) force. Throughout this study, these principles have been treated with an equal importance and any possible violation against the principles has been avoided in the workstation design. The visibility principle was implemented considering interior visibility on the instrument panels and exterior visibility through the top of the steering wheel. As specified in the APTA (1977) "Baseline Specification" commonly called the "whitebook," a minimum visibility marker, an imaginary point in front of the bus (107 cm tall and 61 cm in front of the bus), was used to define the visibility constraint. This visibility requirement can not be violated for safety reasons. The metric visual constraint is geometrically approximated to a 30 downward sight line with a range of less than 3 degrees for the population (Bucciaglia, 19951. Therefore, after determining the locations of DEP from NSRP for the 5th percentile female, the 50th percentile, and the 95th percentile male in the workstation, sight lines were drawn from the DEPs to locate the instrument panels and the steering wheel below the 30 downward exterior visibility requirement. The reach, comfort, and minimum force principles were achieved together in the workstation design by utilizing data on the comfort range of motions (ROMs) of body - 2.~!

OCR for page 11
5 - 4.5 4 - _ . 3.5 _ ~. . 3 Rating 2.5 2 1.5 1 ~ A _._ _ ~443 ~ 0.5 __ _ O Small Med.Large Female FemaleFemale I O - - *4 Small Med. Large Total Male Male Male Population Group Figure 2.22: Ease of Ingress/Egress Evaluation Result of Mock-up The standard deviations for visibility, reach, comfort and adjustability are close to each other at values of about 0.6. The measure of ease of ingress/egress, a topic which many people offered comments, had a larger standard deviation, a value about 1. One reason for this may come from the fact that many jurors suggested that the seat should swivel. However, a swivel seat may not provide sufficient mechanical reliability. The placement of the adjustable components as determined by the jury is tabulated (Table 2.16). This information is helpful in order to determine the actual required adjustment ranges or to verify if a particular adjustment is even required. The table shows that the adjustment of the pedals is so small and thus it may be possible to fix the pedal location without adjustment. - 2.64

OCR for page 11
Table 2.16: Adjustable Components and the Settings from Jury Evaluation Component . Steering wheel Seat (NSRP) Left instrument pane! (NL,IRP) Right instrument pane] (NRIPRP) Pedals (NPRP) Variables Hub Orientation Column Tilt Column Telescope Fore-aft Vertical Fore-aft Vertical Fore-aft Vertical Fore-aft Vertical Mean value 40.4~ 33.3 o - 8.1 cm 90.9 cm * (0.0 cm) 37.6 cm . 67.8 cm* (23.1 cm) 50.0 cm 59.7 cm* (31.2 cm) 59.9 cm 0.0 cm* (90.9 cm) 50.0 cm S.D. . 10.9" 5.90 5.6 cm . 7.6 cm . 3.0 cm 6.1 cm 3.8 cm . 4.3 cm 4.6 cm N/A . ~ 3.8 cm , (Note) The locations of the reference points were measured from the workstation origin (WO) (located on the platform underneath of NPRP) defined in the mockup (see Figure 2.16~. Thus, for example, the average horizontal distance of NSRP from NPRP is 90.9 cm. Later, the definition of the WO was changed to the location determined by projecting the NSRP onto the platform (see Table 2.1 and Figure 2.9) without changing the WO height. The boldfaced numbers are those recalculated from the newly defined WO. 2.3.3 Summary The population was grouped according to their stature and gender. By this grouping, average height of the small female group was close (within a standard deviation) to that for the 5'h percentile female. Similarly, the large male group average height was also close (within a standard deviation) of the 95th percentile male. Therefore, the population extremes were included in the mockup evaluation and, to some extent, over represented when compared to the general population. From the results of the evaluation, three major comments can be made: (~) the workstation is able to accommodate a population ranging from the 5th percentile female to the 95th percentile male, (2) with this implementation of the workstation, the - 2.65

OCR for page 11
evaluation provides a general idea for the amount of adjustment required to accommodate the above population range. For example, the jury evaluation showed that increased seat travel relative to typical production moclels in both fore-aft and vertical directions would be helpful, and lastly, (3) the jury evaluations demonstrated positive indications on the workstation on the average in terms of visibility, reach, comfort, and adjustability. These ratings and their standard deviations were consistent for all population groups. However, the last measure, ease of ingress/egress, had a larger standard deviation than the previous measures. This is indicative of many jurors' opinion that the operator seat should swivel. To remedy this situation, large seat travel should be included in the prototype. - 2.66

OCR for page 11
2.4 JACKS Computer Simulation Computer simulations have been used to verify workstation designs before they are actually implemented as working prototypes. A variety of software tools (SAMME, COMBIMAN, CREWCHIEF, JACK@, etc.) are available to mode] a human graphically and simulate his/her tasks within a designed workstation. These tools provide an analytical way to ensure that the intended users of a workstation will be able to perform their tasks with underlying ergonomic design principles. The bus workstation design was evaluated with JACKS 5.9 in this study. JACKS is a software system for 3-D human modeling and simulation which runs on SG} IRIS workstations. JACKS incorporates sophisticated algorithms for anthropometric human figure generation, multiple limb positioning under constraints, motion animation over a specific interval of time, visibility and reach assessments, and strength performance simulation of human figures (Computer Graphics Research Laboratory, 19941. A detailed presentation of this work is included in Appendix C. The objectives of the computer simulation, in this study, are to: Identify the expected performance of a bus operator in the context of the designed transit bus operator's workstation. Validate the adjustment ranges of the workstation components (seat/ steering wheel/ instrument panels) to accommodate 95 percent of the US adult population presented in SAE IS33 (SAE, 1994), and also to provide sufficient visibility, acceptable reach, and comfortable driving posture for the population while performing the bus operating tasks. Evaluate the bus workstation with a human model simulating the bus operating tasks in terms of - visibility of the displays on the instrument panel and out-of-windows, - 2.67

OCR for page 11
- reach to the steering wheel, the controls on the instrument panels, and the pedals, and - adjustability of the workstation components for the intended user population such that comfortable postures can be maintained while driving the bus. 2.4.1 Simulation Mode] Development The three human models (5th percentile female, 50th percentile, 95th percentile male) were created using the anthropometric data set designated in the SAL IS33. Since the SAE anthropometric data are not sufficient to specify a complete 3-D human mode} in JACK@, unavailable anthropometric data were found. The unavailable data were mostly anthropometric dimensions related to thickness and circumference of body parts, which were of less significance in the evaluation of workstation design in terms of visibility and comfortable reach. ~ order to complement the anthropometric data, NASA (1978) and ARMY (1988) anthropometry studies were referred and applied to the analytical determination of the missing data by assuming the proportionality of human body dimensions and a cylindrical shape of body parts as discussed in Appendix C. Seventeen typical bus operating tasks (Table 2.17) identified by the bus operating task analysis (discussed in section I.2 Operator Task Analysis) were simulated for the human models in JACKS. During the simulation of the bus operating tasks, the human model motions were governed by a set of virtual kinematic constraints related to each bus operating task. For example, during the simulation related to steering wheel maneuvering, the hands were constrained on the steering wheel to identify the upper-limb joint configuration; in the simulation corresponding to pedal activation, the right foot was restricted to the brake or accelerator pedal and the hip pivot point was fixed to a designated location over the seat according to the SRP and hip pivot point relationship (see Figure 2.51. - 2.68

OCR for page 11
Table 2.17: Example of Bus Operating Tasks and Metrics Bus Operating Task ~ pre-c riving task on-road driving task picking-up/ depositing passengers seat adjustment steering wheel adjustment transmission engagement parking brake release four-way flasher activation kneeling activation Adjust the seat horizontally and vertically in relation to the pedal location. This is to ensure that a mannequin maintains its comfortable hip, knee, and ankle orientation. Metrics comfort, adjustability Tilt and telescope the steering column, or tilt the steering wheel based on the seat position maintaining the static driving posture and the 30 degree downward visibility requirement simultaneously. Shift the bus into gear on the left instrument panel. Release the parking brake on the right instrument panel. Activate the four way flasher on the right instrument panel. Evaluate the activation postures of the right arm and the visibility of the four way flasher. Activate the kneeling mode on the right instrument panel. Evaluate the activation postures of the right arm and the visibility of the kneeling switch. . .. . . v~S~bi Ity, comfort, adjustability . .. . . vlSlbl. .lty, reach, adjustability visibility, reach, adjustability . . . . vlslblllty, reach, adjustability visibility, reach, _ adjustability During the simulation, the bus workstation was evaluated in terms of visibility, reach, comfort, and adjustability. To facilitate this workstation evaluation, the simulation system generated two types of output files at the end of each bus operating task; one recorded the body joint angles of the human model, and the other recorded the selected locations of the workstation components. The simulation system developed utilizing JACK@' s capabilities allows a user to: Setup the simulation environment such as displaying site labels, shading windows, generating orthogonal windows, and displaying rulers between sites. . . Select a 3-D human mode] among three population groups which are pre-defined by using the anthropometric data from the SAE 1833. Manipulate the locations of the adjustable workstation components (seat, steering wheel, instrument panels) interactively. Simulate motions of the human figure which are controlled through a set of kinematic constraints for 17 bus operating tasks. - 2.69

OCR for page 11
Create simulation result files which include the postures of the human figure and the specified adjustment values of the workstation components for each bus operating task. and Execute simulations of the bus operating tasks through either an interactive mode or a batch mode. 2.4.2 Simulation and Design Validation The simulation started by importing the workstation components from a CAD environment and integrating them with a 3-D human model. The human was located on the seat using the H-pt and SRP relationship (Diffrient et al., 1981~. Simulating the bus operating tasks under the kinematic constraints previously declared, the adjustable components were located iteratively until the human-workstation mode] satisfied ergonomic principles such as visibility, reach, and comfort. The locations of the components and joint angles of the human were recorded in result files. The workstation design was evaluated in terms of visibility, reach, comfort, and adjustability by observing human motions during animation and analyzing the resulting posture files. Based on the evaluation results, design modifications were made to improve the workstation design. Evaluation results regarding visibility, reach, comfort, and adjustability for the steering wheel adjustment are illustrated as an example in Table 2. ~ 8. - 2.70

OCR for page 11
Table 2.~: Workstation Design Simulation for Steering Wheel Adjustment Task | steering wheeladjust]nent Task Category adjusting workstation components Tilt and telescope the steering column, or tilt the steering wheel based on the seat Scenario position maintaining the static driving posture and the 30 downward visibility requirement simultaneously. . ==1 ~ ~ _I [ ~ . , ~L 1 1 111511~_ 1. _ __ If_ L 1 1~ ~ _~61~ ~1 mustrabon ~ _ ~ ~_ 1 ~1 ~1 steering wheel column tilt 10 deg (clockwise: +, counterclockwise: -) i Design Values steering wheel column telescope 11 cm (upward +, downward: -) steering wheel hub tilt 10 deg (clockwise: +, counterclockwise: -) Simulation Results Population Group ~=~_ column tilt 5 O O o telescope -5.5 cm 0 cm hub tilt -5 O o shoulder flexion 21.8 (4) 29.9 (2) shoulder abduction 4.1 (4) 7.6 (5) shoulder rotation 24.3 (4) 9.5 O (5) elbow flexion 56.9 (5) 45.0 O (4) wrist flexion 0 (5) 0 o (5) visibility 5 . . reach 5 5 5 comfort 4.4 4.2 adjustability 4.7 Remarks l - 2.71 95 th Percentile Male 5.5 cm s o 30.8 (2) . . 1 5 2 (5) 143 ~4) 45 7 O (4) o o (s) 4

OCR for page 11
The adjustment ranges shown in Table 2.19 were validated through iterative design modifications and simulations. Table 2. ~ 9: Adjustment ranges of workstation components tested in simulation Design Variable Ad ustment Range ~J ~ Seat Horizontal 18.5 cm (7.3 in.) Vertical 6.7 cm (2.6 in.) Seatback Angle 10 deg. Steering wheel Column Tilt 10 deg. Telescope ~ I.0 cm (4.3 in.) Hub Tilt 10 deg. Left Instrument Panel Horizontal 9.9 cm (3.9 in.) Vertical 4.0 cm (1.6 in.) Right Instrument Pane! Horizontal 13.3 cm (5.2 in.) Vertical 4.5 cm (~.S in.) 2.4.3 Summary A computer simulation mode] was developed to validate the bus operator's workstation design. Utilizing JACK~'s capabilities, the simulation mode} provided the following functions: setup of simulation environment. selection of human models with the SAE 1833 anthropometry. adjustment of workstation components. simulation of bus operating tasks under specified kinematic constraints. creation of simulation result files. mode! execution in an interactive mode or a batch mode. The SAE 1833 anthropometric data were used to generate three different size human models (5th percentile female, 50th percentile, 95th percentile male). Estimations - 2.72

OCR for page 11
were made to complement unavailable anthropometric data for three dimensional human modeling. The simulation system was designed to simulate 17 typical bus operating tasks. The simulation system determined the expected behavior and visual field of a human for each bus operating task in the context of the workstation. The human behaviors were controlled by the designated kinematic constraints during simulation. In simulating each bus operating task, the locations of the workstation components were manipulated within the adjustment ranges. Design modifications were made wherever inappropriate design was found. The designated adjustment ranges were evaluated with respect to the degree of satisfying ergonomic requirements such as good visibility, acceptable reach, postural comfort, and sufficient adjustability. A valid transit bus operator's workstation design was produced through iterative design modifications and simulations. Also, animation of the bus operating tasks facilitated the evaluation of the workstation in dynamic situations. - 2.73

OCR for page 11