The following is an abridged version of a paper that was presented at the Computer Technology Solutions Conference in Detroit. This concept offers an innovative method of reducing ergonomic impact in advance of physical construction.
_________________________________________________________________ To obtain an unabridged version of this document send an email to JimR.USA@gmail.com ask for a copy of RACECR
Ergonomic Analysis in the Virtual Factory
Rapid Analysis Concept for Ergonomic Cost Reduction
A method of reducing manufacturing costs through the application of rapid, rough-cut analysis
tools that can be applied to conceptual manufacturing processes and to virtual product designs
James J. Reid
The methods and concepts described herein represent a breakthrough approach to ergonomic injury reduction that is currently being evaluated by Xerox. The objective of this approach is to reduce the overall ergonomic stress in the factory by analyzing the workplace in the virtual environment and thereby reduce the number of ergonomic injuries. This concept contends that in addition to providing a substantial reduction in direct operating cost, involvement in ergonomic analysis in the early part of the design cycle will improve awareness of better ergonomic design principles and promote development of friendlier and faster assembly methods.
The contents of this paper are intended to be a guide that manufacturing operations can build upon to establish an injury reduction program. The concepts and unique rules presented in this paper should be evaluated for their appropriateness in each factory environment before they are applied. The Rapid Analysis Concept for Ergonomic Cost Reduction – RACECR (pronounced “racer”), presented here is a method of accelerating the process of bringing new products to market by examining a work environment for ergonomic stress in its virtual state. This tool is to be used as an overlay to other analysis techniques that may currently be in use. Key components of the RACECR system are the ErgoSample and ErgoStress analysis methods that are used to evaluate and correlate actual factory environment risks with those in the workplace concept model.
A large body of Human Factors/Ergonomics knowledge has been acquired through research over the past sixty years. Although this knowledge has become more available through a growing number of field experts and through government guidelines, in practice, companies are generally reactive rather than proactive in its application.
At Xerox we have developed a new method that incorporates the structured integration of human factors/ergonomics data and newly available software tools. This enables proactive application of human factors/ergonomics knowledge throughout the design process, for both products and the factories that make them.
The payback for conducting ergonomic reviews early in the design cycle is more than just reducing injuries. Making ergonomic corrections in the production environment can cause production delays, and often means implementing a “fix” that can increase the cycle time. Conversely, introducing ergonomic awareness to a product BEFORE it enters its production phase gives us the freedom to explore ergonomic solutions using better designs and better methods. A better method ergonomically is also a method that is easier to perform, and a method that is easier to perform is usually a faster method.
Increasing market demands for rapid paced introductions of lower cost, high functionality products has created pressures for more rapid product development and a need for factories to achieve high product volumes in the shortest possible time. These market changes dictate that we begin delivering bug free products to the factory. The factory must, in turn, deliver defect free products on time to the customer. One barrier to these requirements is the impact of ergonomic problems in the workplace.
Ergonomic problems bear a high price tag not only in the tangible cost of compensation and lost time, but also in the less obvious cost of their impact on the product delivery schedule. Product delivery delays are created by the need to make corrections to a production line after start-up and often after product launch.
In recognition of this problem many companies are now fully engaged in ergonomic risk reduction programs however, most efforts to this point have concentrated on analyzing work areas where problems have been reported.
If an ergonomic problem reaches the production floor, we are too late. Fixing ergonomic problems as they surface is like stepping on cockroaches. We can’t hope to eliminate ergonomic risk by studying a workplace that already has a problem. We need to change the climate by optimizing work environments through better product, workplace and process designs.
New ergonomic analysis software tools are finding their place in many companies. The perceived value of these tools varies widely depending on the cycle times and what types of products are manufactured. These tools are designed to produce a posture analysis plotted against time, then produce reports that a knowledgeable person may review to identify ergonomic risks. Some software tools attempt to give black and white answers to gray questions, while others smother the user with data that requires further analysis.
The purveyors of the tools are not equipped to counsel us in the optimum method of integrating these tools into our business process partly because the work in each part of every factory is unique. If your business process lends itself to analyzing a factory in its entirety using one of these software tools, then you should analyze your factory in its entirety. Most of us will find that type of resource commitment impractical.
Figure 1 - Hypothetical costs - omitted
Despite all the logical and moral reasons we can give about why we want to exceed the guidelines to provide a safer work environment, we must also keep in mind that our arguments are going to be difficult for senior management to embrace unless they can be backed with projections of a positive profit impact.
3.REVIEW OF RELATED WORK
Although first identified more than 200 years ago by Ramazinni who identified “certain violent and irregular motions and unnatural postures of the body …that serious diseases gradually develop therefrom.”, Ramazinni in Putz-Anderson (1988) Cumulative Trauma Disorders, and although studies in the early 1900’s provided conclusive documentation that ergonomics affects performance and is related to operator injuries, interest in the topic is growing as of late. An increasing number of articles about ergonomics are appearing in a broad band of seemingly unrelated periodicals. Several factors seem to be driving this interest. One of the key factors is a painful awareness of the true cost of ergonomic injuries to industry.
The United States Department of Labor, Bureau of Labor Statistics reports that Cumulative Trauma Disorders (C.T.D.’s) account for over 60% of workplace injuries; up from 50% in 1988. According to the Occupational Safety and Health Administration (O.S.H.A.), one major reason for these increases is more accurate records keeping.
The implication of this statement is that the costs have been with us all the time. With this in mind, we can appreciate the need to reduce ergonomic costs to stay competitive in today’s economic environment. D. Alexander stated in his article Strategies for Cost Justifying Ergonomic Improvements (IIE Solutions, March 1998) “The cost of correcting ergonomic design at the initial part of a design is about 10 percent of the cost that will occur later”.
Figure 2 - Relationship of Productivity and Quality to Occurrence of CTD's - omitted
Melissa Larson, Senior Editor for Quality Magazine says “Well-designed workstations aren’t just a smart health and safety decision-case studies show they also make workers more efficient.” (Ergonomic Workstations Boost Productivity, Quality, March 1998). This article steps through an analysis where a 62 percent reduction in task cycle-time is achieved by making the workcycle more operator friendly.
Researching information about ergonomics is bound to leave an engineer with a certain amount of frustration. The problem seems to grow larger as we become more familiar with ergonomic principles. Interdisciplinary involvement is needed for a complete solution and interdisciplinary involvement is not easy to control. An article in IIE Solutions magazine from July 1998 talks about “A Diversity of Needs” with regard to software analysis tools stating that “Sometimes there is a trade-off between the analyst knowing ergonomics or knowing the job.” (Steven L. Johnson, Selecting Computer-Based Ergonomic Tools, IIE Solutions, July 1998). This same article presents a list of leading electronic analysis tools and offers information and selection criterion to guide consumers through the selection process.
There are three primary areas we need to focus on to bring success to an ergonomic program. The first is records keeping, the second is data gathering, and the third is analysis. In another article from IIE Solutions, M. Ousnamer states “Without good data a good solution is a hit or miss process at best” (Ergonomic Solutions Begin with Good Data, IIE Solutions, March 1998). The analysis portion of the formula is where things get a little cloudy. Each factory and each individual manufacturing venue within the same factory, present unique workcycles and a unique set of ergonomic concerns. To fully appreciate this fact we must consider the human organism in its entirety. The study of body interactions is biomechanics. T. J. DeGasperis, D.C. and G. J. Mascilak, D.C., P.T. (Functional Biomechanics, ‘In Practice’, Jan/Feb 1996) define Functional Biomechanics as “…the science that enables us to understand the totality of the human organism and the relationship and interactions that the various body parts, segments and systems have with each other that contribute to the ability or inability to function.” “…In order to properly understand the concepts involved in biomechanics we must fully realize, everything we do, every action we take requires system function.”
Scott Bautch D.C. and Steven Conway D.C break ergonomic analysis into three types that they term as Easy, Complex, and Consultative (Industrial Interaction, ‘In Practice’ May/June 1996). “Consultative” involves matching operators to the job (with consideration for the Americans With Disabilities Act of 1990, see article by the same authors in the November 1995 issue of the American Chiropractic Journal titled ADA and Medical Examinations).
A Bautch/Conway “Easy” review is described as “Note the different non-neutral body positions and see if the reason for the position is mechanical or human. By that we mean is there an actual mechanical reason for the position…” or is the person “…placing the body part in an abnormal position.” The “Complex” analysis is the type that “…involves time study design, line design, tools…” etc.
The methods described in this paper conform to the Bautch/Conway “Complex” and “Easy” analysis definitions. A good company ergonomic training program can reduce injuries by bringing focus to the “Easy” category. The “Complex” category requires higher evaluator skills.
4.DEFINITIONS AND EXPLANATION OF TERMS
Human Factors vs. Ergonomics
Human Factors/Ergonomics is the art and science of designing tasks and workstations with the worker in mind...
Human factors and ergonomics by definition are the same, differing only in the geographic origin of the science. Through common use these terms have become somewhat divergent. The human factors technical discipline is commonly associated with industrial design and the human interface with the product. The science of ergonomics is more often associated with the manufacturing environment of operator work sequences and manufacturing equipment. In this paper we do not distinguish between these terms.
It is important to recognize the different elements of ergonomics and it is important understand the subtle differences and dependencies of the various elements of the ergonomic environment. In the end it all fits together. Ergonomic concepts must be applied to all parts of the product design and manufacture. A product needs to be designed with manufacture, assembly, disassembly and service in mind. The workplace design and layout must be ergonomically correct. Ergonomically safe tools and equipment must be specified and the work process must be constructed with an awareness of human factors/ergonomic principals.
Figure 3 - Conventional “Linear Product Development” compared to the “Accelerated Ergonomic Product development cycle” - omitted
Traumatic injuries occur from a single source, usually from a single incident and include cuts, bruises and broken bones. Reducing ergonomic stress in the workplace will have an effect on the number of traumatic injures reported. The relationship of these entities is not easy to discern and is not important to this discussion.
Ergonomic injuries are those that occur from sustained exposure to stress over time. The key differentiating factor between traumatic and ergonomic is TIME.
Lifts can be evaluated for ergonomic risk through the application of a lifting equation provided by the National Institute of Safety and Health (NIOSH). The NIOSH equation determines a Recommended Weight Limit (RWL) for the lift being evaluated. The equation evaluates the effect of lifting on the workers back and whole-body muscles, joints and tendons. It considers the weight of the object being lifted, body posture and the number of repetitions that occur over time.
The NIOSH lift equation determines a weight limit based on time but does not take into account the combined effect of other stressors and activities. To evaluate these other factors we need to look at this potential for cumulative trauma separately.
When to analyze a lift?
Lifts should be evaluated where the weight is significant, the lift involves awkward postures or the repeating workcycle is short. The following recommendation was derived by the author from review of lift conditions that are typical in many factory environments.
At minimum, lifts should be evaluated using the NIOSH lift equation if:
W > 10 lb. Weight is greater than ten pounds or, T < 2 seconds Time between lifts is less than two seconds or, T < W The numeric value of Time between lifts is less than the numeric value of the Weight being lifted Where W = Weight in Pounds and T = Time between lifts in seconds
In the observation of a workcycle, significant weight or force can be recognized by a hesitation in the operator’s motion as muscles tense to overcome resistance. Lift analysis results should be kept as a permanent record to establish the baseline for future ergonomic audits. A good place to keep this information is in the work measurement record for the operation. In this way, the lift information can easily be reviewed when the workcycle changes.
Repetitive trauma injuries, disorders and disease
Terms you may see are Repetitive Stress Injuries-RSI, Cumulative Trauma Disorders-CTD, and Repetitive Trauma Disorder/Disease-RTD. All of these terms are the same. They refer to injuries that are the result of repeated ergonomic insult. Systematic evaluation of workplace procedures using a software tool can help an analyst identify workcycle components that expose an operator to a risk of repetitive trauma injury that may otherwise be difficult to detect. If evaluation tools are to be applied by a non-ergonomist e.g. an Industrial Engineer, the applicator needs adequate training. An Industrial Engineer using a Methods Time Measurement (MTM) system to develop a work measurement study gains all of the information needed to evaluate an activity for this type of risk when performing a motion analysis. Ergonomics training of an engineer does not, however, mean that the engineer will be able to do a time-based evaluation of a workstation without using some method or tool that requires a significant additional amount of time to apply.
There should be no expectation that a manufacturer can reduce ergonomic cost without applying some resources to that effort. Although simply throwing resources at this problem will undoubtedly show some results, a structured plan is needed to guarantee that allocation of resources will result in a significant improvement in company profits.
Design For Ergonomics (DFE)
Designing products that can be manufactured, assembled, serviced and remanufactured in an ergonomically safe manner requires a design for ergonomics program that embodies training, standards, research and lessons learned feedback from downstream operations.
One principle of reducing ergonomic stress through better design is to eliminate the need for special tools to solve ergonomic problems. If a tool is added to a process to reduce ergonomic stress, we can’t always assure it will be used in the assembly environment, and it will seldom be available in service or remanufacture environments.
DFE case study:
Wire ties with a clip that pushed into a hole were used extensively in the factory. The push-in component required a high force to install. A push-in tool was provided to operators. Despite operator recognition of ergonomic risk from push-in by hand, the tool was seldom used because it was faster to push in the ties by hand. After installation of the wire tie, the wires were bundled and the tie was cinched-up to hold the bundle in place. Again a tool was provided that operators seldom used. In response to a number of ergonomic injuries, a clip that could be slid into a slot with little force was selected to replace the ties. With the new clip, wires are fed into the clip as they are assembled, clearing them out of the way instead of having to wait until all wires are assembled. The result was the elimination of ergonomic risk and a significant saving of assembly time.
Ergonomic Risk Assessment and Reduction
Risk Assessment is the analysis of a workplace for the purpose of finding specific activities that expose operators to ergonomic risk.
These activities may include any of the following ergonomic warning signals:
•Joint deviation (e.g. wrist, shoulder elbow) near or beyond its normal motion limit •Frequent manipulation of moderate to heavy weights •Frequent application of moderate to heavy pressure •Awkward postures •Cycles where the operator frequently moves outside of the normal reach zone •Similar movements repeated frequently within a task •A single body part that does not rest (constant motion)
The potential for ergonomic risk can be evaluated using manual methods or with an ergonomic analysis software application.
Ergonomic analysis software applications are the most effective tools for determining the level of risk that an activity poses to the operator.
Following a risk assessment, revisions can be made to products, workplaces, tools, and work processes to reduce or eliminate ergonomic risk.
Ergonomic Stress Assessment and Reduction
Reducing overall ergonomic stress is an important, but not often recognized, part of designing safe workplaces. Stress reduction is used with risk reduction to improve the work environment. The methods introduced in this publication focus on ergonomic stress assessment and reduction. As stated previously, ergonomic injuries are those that occur from sustained exposure to stress over time. Ergonomic stresses have a cumulative effect beyond the effect on a body part that may be identified by an analysis.
Although many ergonomic stress factors are on the list that we use to determine a fatigue allowance for a work environment, Increasing fatigue allowance is not an effective means of accommodating ergonomic stresses. Fatigue allowance is time added to a workcycle in recognition of the fact that when an operator gets tired he or she will slow down. Just adding time to a workcycle does not assure that operators will pace themselves or exercise reasonable caution.
There are other factors that diminish the effect of allowances over which we have little influence. Some of these factors are, company incentive programs, peer pressure, desire for an early quit, break and lunch-time activities, after work recreation, machismo and personal pride. The best way to deal with ergonomic stress is to eliminate it where possible and reduce the level of risk for any remaining ergonomic stresses. Changing a workplace design to improve anthropometric accommodation, distributing stressful activities over a broad time period, or dividing stressful activities between multiple workers are all effective ways of reducing ergonomic stress. The largest problem remains how to identify ergonomic stress in the first place.
Since cumulative stress is mapped to a time period, it often can’t be found through casual observation.
Injury Records Database
Record keeping is an OSHA required part of doing business. Examine the level of detail that is contained in the injury records. Knowing the source and profile of injuries can lead us to find solutions. Things you might want to know: specific activities that contributed, specific body part affected, and specific injury. The database should be central and have search and sort capability to help locate the source of injuries.
Part and Work Station Visualization Tools
3-D geometric modeling and kinematics, digital humans and dynamic simulation tools can help with visualization of the virtual factory. These tools can help ergonomic experts better understand the workcycle.
Work Measurement and Ergonomic Evaluations
Work measurement techniques that analyze operator motions, such as MTM, are used to predict the labor cost of a workcycle. The product of the work measurement effort is used to determine Unit-Manufacturing-Cost, and to assist with line layout and staffing assessments. Accurate time standards are an essential ingredient to many business decisions. In the virtual environment, time paced discrete event simulation and workplace ergonomic analysis applications are newer additions to the list of customers of a work measurement analysis.
Choosing an Electronic Ergonomic Evaluation Tool
Some commercial ergonomic analysis offerings are tools that allow the applicator to derive a time standard and an ergonomic analysis from a single motion analysis. Logically, this is a sound approach, since the information needed to generate a time standard is the same information that is needed to generate an ergonomic analysis. The major disadvantages are the length of time needed to obtain a study, and the level of training, experience and awareness that an applicator needs to acquire to become proficient in both areas. Because of the amount of motion detail needed, applications of this type are usually based on MTM-1, which, in itself, requires a great deal of application time, training and experience to apply. This type of application tends to be most useful where cycle-times are short.
Other applications are stand-alone systems or overlays. An overlay is a linked application where a work measurement study is performed, and the time and sequence information is passed into a separate ergonomic analysis application. The major advantage of these systems is that a much faster handling standards application method can be used, shortening the amount of standards generation time needed. This also allows the standards information to be passed into the business process before the ergonomic analysis has been completed. Some stand-alone applications are specialized tools that are designed for use primarily by expert analysts.
The selection of an application for your business should be dependent on how well that application fits into your business process.
6.APPROACH TO THE PROBLEM
Conventional Use of Ergonomic Tools to Analyze the Virtual Factory
Newly available ergonomic visualization tools are gaining acceptance in many factories. These tools include 3-D solid modeling packages that may include dynamic view rotation, exploded view generation and various types of kinematics motion modules. Manufacturers expect economic gains from the use of these tools on the part geometry side of the product development cycle. These tools can also be used to assist in the analysis of products and workcycles for ergonomic quality. Part geometry from a CAD system can be re-used to create a virtual workstation. At this point the workstation can be reviewed for human factors. Once the work process is defined, the workplace/part geometry can be passed to a discreet event simulation product. To obtain accurate results from the simulation model, an MTM analysis or other time estimating method must be employed to determine the cadence of the simulation. Here an anthrometrically-based digital human can be inserted and programmed to accurately depict the operators’ work sequence. The human model can generate information that will assist in evaluation of the workplace and help establish the level of ergonomic risk in a workcycle. This sequence allows qualified ergonomic evaluators to be included in the product development cycle.
The Need For A Rapid Rough-Cut Ergonomic Analysis System
Although the conventional method sequence is good, by itself, it is too lengthy. By the time the digital human is walking around in the virtual factory, metal is already being cut for parts and tools and building space allocations are firm. If an ergonomic problem is found at this point, it will most likely be dealt with in the same manner as an after start-up problem rather than researching its root cause. In addition to this path, a rough-cut preview method can be used to reduce the potential for discovery of ergonomic problems late in the development cycle.
Before the product was approved, a cost estimate that included a labor cost was prepared. At that point, a visualization of the work sequence was formed; most likely it existed in a few pencil sketches and in the estimator’s mind. This may be the first opportunity to review the factory for ergonomics. The activities associated with early product cost estimating can be extended to determine ergonomic risk.
7.RACECR - RAPID ANALYSIS CONCEPT FOR ERGONOMIC COST REDUCTION
The RACECR system provides tools and a methodology that can help deliver, at production start-up, an ergonomically safe work environment to the factory.
An application engineer using RACECR evaluates the level of ergonomic stress in a physical factory work environment using ErgoSample, then compares the data gathered to actual injury reports for the same area. Once a correlation between observed and actual has been established the ErgoStress technique can be used to evaluate a conceptual workplace of a similar type. In the conceptual workplace, particular attention is paid to reducing stress in areas associated with a high number of incident reports in the physical factory.
In 1994, a task was undertaken to analyze workplaces for ergonomic safety as part of a project for the U.S. Government. Though the work sequence was known, workplaces existed only in a few not-to-scale sketches. The analysis was undertaken with assurance of assistance from several large corporations, each of whom had a reputation for being leaders in human factors and ergonomics. After a few phone calls it was noted that none of the companies involved had any experience analyzing virtual workstations.
Information and methods about ergonomic analysis were collected. A great deal of commonality was noted but each method was based on observation of a physical workplace. The first step in the virtual workplace evaluation began with a motion analysis of the workcycle using MTM. With good Industrial Engineering resources, the workcycles were reviewed while visualizing the operator motions and then plotted against time. Next a check-sheet analysis was performed. It soon became evident that the check-sheet process generated a huge pile of paper that couldn’t easily be correlated to virtual events and therefore didn’t lend itself to review of the workcycle for improvement. Most importantly, the project had strict records keeping requirements that the loose, unrelated documents didn’t conform to.
The solution backed into the problem. With records keeping as its initial goal, the final result was development of a complete analysis system. The solution included an analysis method that broke the workcycle into small segments and recorded the highest stress ergonomic incident in each stress category. There was an expectation that the statistical accuracy of the analysis would be developed through a significant number of virtual “snapshots”. Single high stress incidents were recorded and analyzed separately. The results were as expected. This method is the basis for the ErgoStress analysis procedure that is presented here as part of the RACECR system. A companion system, named ErgoSample was also developed to evaluate existing workplaces. The name RACECR was coined to embody the philosophy, and to differentiate early analysis activities from those occurring later in the product development process.
The RACECR theory assumes that there is a relationship between the statistical frequency of occurrence of ergonomically stressful activities and the actual number of injuries that are reported.
Based on this assumption:
a)Reducing the overall ergonomic stress in an operation will result in a reduction in the number of injuries that are reported. b)Statistical information about this relationship can be gathered, and that knowledge can be leveraged to improve work environments by analyzing them in their virtual state before production start-up. Recognition of this relationship between the virtual and physical factory is the engine that drives the RACECR system. c)The behavior of these relationships will be predictable.
In time, a better understanding of these relationships can be used to improve the quality of the tools used to analyze virtual workplaces. By auditing the result when a new product goes to the factory, the scoring methods used, in both data collection and evaluation can, by iterative adjustment, be made to better represent the physical environment.
Components of the RACECR analysis system
The RACECR system encompasses good practices already in place in most companies, and includes some new tools that help link the components together. Listed below are some of these components: Design For Ergonomics program (DFE) ErgoSample, a unique current state evaluation method An ergonomic injury tracking database An ergonomic evaluation system (software or manual) NIOSH lift evaluation capability. Even if the ergonomic evaluation method includes a lift evaluation module, a separate application may be desired to gain wider use. A work measurement technique capable of determining operation time without observation such as a Methods Time Measurement (MTM) system. ErgoStress analysis, a method of applying the information gained from ErgoSample to the virtual factory. Virtual visualization products such as 3-D modeling, Kinematics, Virtual humans, View and markup, Discrete event simulation modeling etc.
The unique components of the RACECR system are ErgoSample and ErgoStress.
RACECR is a rough-cut measurement system that provides ergonomic information to the early part of the product development cycle. The RACECR method can be used concurrently with conventional analysis methods where ergonomic analysis activities are triggered by key events in the product development cycle.
The ErgoSample data collection and scoring system
Existing production work places can be randomly observed and the occurrence and severity of ergonomic stress can be recorded. The recorded severity is given a numeric value. A sufficient number of observations need to be made so that a statistical confidence is achieved. The recorded stresses can be plotted against the time period of the observation and the result displayed in a pareto diagram to determine the most common ergonomic risk factors. As part of this effort, an ergonomic “score” for the workplace can be determined. The score is the numeric total of observed ergonomic stress compared to the reported actual injury rate for that type of operation. The ErgoSample method in the RACECR system is a simple method based on commonly known work sampling techniques.
Work sampling is a work measurement technique where random observations are taken over a period of time. An observer visits workstations according to a schedule and records the work element that is occurring at the instant of each visit. The number of observations needed to obtain a statistically valid study is based on the deviation and distribution of the observations. The percentage of distribution of the various elements, as they occurred during the random observations, tends to equal the percentage of time spent on these activities that would be found by continuous observation.
Using this same technique, the occurrence and type of ergonomic stress can be sampled with similarly accurate results. One of the big differences between work sampling and an ErgoSample is that the observer in an ErgoSample does not need to be familiar with the workcycle. Care should, however, be taken to assure that extremely rare occurrences, such as a machine being overhauled, are frequencied at the appropriate interval. An activity that may occur only once a year, would be averaged by the number of workdays rather than the exact observation frequency. In an ErgoSample, breaks are included in the observation frequency. A spreadsheet can be useful for this evaluation. Random number generation and statistical accuracy and confidence calculations can be imbedded in the sample results tally form.
To conduct an ErgoSample analysis, a scoring system must be developed from known types of simple, observable, ergonomic contributors such as reach, bend, and lift followed by a severity rating. The ErgoSample scoring system may be patterned after the ErgoStress scoring system described later in this paper. See Figure 5
An existing operation is sampled at random intervals. The sample variations are evaluated to determine how many samples are needed to obtain statistically significant results. Once a stable sample is obtained the result is compared to injury reports on that operation to obtain an ergonomic “score”. The process is repeated in a different venue and the results from both studies are compared. The scoring system (the weight applied to each type ergonomic observation) is adjusted until an accurate correlation between the observed events and the injury rate is established. The system can then be applied to the virtual environment. In the virtual environment “experiments” can be conducted to find better methods that will reduce the score. Once the product goes into production, a post-audit is conducted to see how well the predictions matched the results. From the post-audit the lessons learned are fed back into the system to improve the results.
Figure 4 - Data Development - omitted
In stepping through this process the accuracy of the results are concentrated as though they are moving through a funnel. The repeating process becomes a normal part of doing business with two valuable results:
1)Designing what-if experiments in the virtual environment gives us an opportunity to find ergonomically better methods. 2)Giving engineers a method of reviewing the work process will help them find ergonomic “hot spots” which they can resolve and/or ask an ergonomist to review.
An ErgoSample evaluation can show us exactly where to look for key contributing ergonomic factors when reviewing a virtual factory. Next, a process will be constructed that will find the causes of ergonomic stress at the product and factory design level. Where possible, we may wish to implement change in the existing production environment. One of the more important benefits of ErgoSample is having the ability to demonstrate improvement.
ErgoSample observation example
For this example we will assume a current reported ergonomic injury rate of one per fifty-three employees.
An average factory has 1 ergonomic injury report per 10 employees per year. The benchmark level is 1 reported injury per 160 employees. This example was selected as typical of assembly operations at a large firm.
The time needed to make an observation tour, expressed in minutes/number of observations, is 1 observation per 10 sec or 6.0 observations per minute
The injury rate in our example factory is 1 injury/53 employees therefore the rate is = 1.89%. Therefore if each worker works 2000 hrs / year there will be one injury per 106,000 hours of work.
If, on a 4-minute walk through our example factory, 24 observations were taken and scored 0 through 3, where 3 represents high stress, and the total of the scores equaled 10, we could compute a relative value for comparison.
Total score = 10 per 24 observations in 4 min. -or- injury rate/employee = 10/24 (10 total score/24 observations) = 0.42 -therefore- 0.42 is equivalent to 0.0189 (1.89%) injuries/ employee.
Ergonomic improvements are then made to our example workplace and the area is re-evaluated. After improvement the ratio changed to 0.33 (8 total score/24 observations) then the new expected injury rate should be:
0.42 = 0.33therefore 0.0189*0.33 = 0.42*? -or- ? = 0.0189*0.33 -or- ? =0.0149 0.42
In this example the expected incidence of ergonomic injury has changed from 1.89 % to 1.49 %, therefore the incident ratio has changed from 1 per 53 to 1 per 67 employees.
If the ergonomic injury cost for this factory was $10M/yr. then the savings would be $280,000/Year (YOY)
A realistic target is a 20% reduction in ergonomic injuries per year. For a company with an ergonomic cost of $20M/year, this type of savings could mean a reduction in operating costs of $1000/minute.
The ErgoStress evaluation model and scoring system
ErgoStress is a method of approximating the ergonomic stress level of an operation without a need for direct observation. The method is designed to produce a rapid evaluation of a virtual workcycle.
An ErgoStress analysis will help locate repetitive time-sequence ergonomic risks. It will NOT locate violations of sound ergonomic principles, therefore, the first step in a virtual workplace evaluation is to review the work sequence and workstation concepts for ergonomic best practices . An ErgoStress analysis can then be applied to point to time-sequence ergonomic risks. Following this analysis the highest risk work sequences may be further analyzed using an ergonomic analysis software .
An example of an ErgoStress scoring sheet is shown in figure 5. It is important to note that all possible ergonomic environment contributors are NOT included in this because stressors like metabolic, vibration and temperature were not concerns in the example operation.
To use the ErgoStress technique, the work process is broken into workcycles that represent the approximate amount of work that one operator will perform. Each workcycle is then divided into functional work units or elements. These smaller elemental work-segments should be approximately equal in duration. For shorter workcycles, use elements that are each about ten percent of the operation time. For longer cycles (>10 min.) the segments should not be more than one minute in length. Each work-segment is evaluated for ergonomic stress content, and each occurrence of ergonomic stress is recorded. The scores are tallied and a rating is given to indicate the amount of ergonomic stress in that workcycle.
Operation sequence for an ErgoStress analysis:
1.A work measurement analysis is completed and lifts are evaluated using the NIOSH equation. 2.Review the work measurement analysis for ergonomically stressful activities by examining the workcycle and for non-neutral body positions that are interjected by the workplace environment. Non-neutral body positions are those that are dictated by the work environment or the type of operation being performed. This review conforms to the Bautch/Conway “Easy” definition as described in Section 3. Review of Related Work.
3.Ergonomically stressful activities are marked (not scored at this time) and the time in each element for these activities is tallied to yield the total time spent performing ergonomically stressful activities. The total is then recorded in the column labeled “Ergo TMU” in the example. Time units in this example are TMU’s. A TMU is 1/100,000 of a hour 4.The total of the “Ergo TMU” time for all elements in the station is compared to the “Total TMU” time for the operation being evaluated. The resulting figure is the “Ergonomic demands, percent of workcycle” for the operation. 5.Using the scoring system shown, review the motion analysis for each element and locate the highest stress incident in each category, then mark the score symbol in the appropriate row/column in the table.
6.The next step is to develop the profile of the ergonomic stress. A flat score of 0, 1, 2 can be assigned to the Low, Moderate, and High categories respectively if ErgoSample data is not available. If the ErgoSample profile has been developed, the category scores are adjusted to match the actual factory profile. 7.The “Ergo TMU” for each element is then multiplied by the frequency that the element is performed and the numeric “Score” assigned to the assigned symbol. 8.The (0-1-2) value assigned to scores in each category row is now totaled for each column, then divided by the number of element rows to determine the symbol representing the average score for each column. That symbol is placed in the “Ergonomic score based on percent of cycle per day” row/column. (If operation is performed for less than 2 hours per day, the work may be averaged with other work the operator normally performs.)
After the workstation has been studied, the sum of the column totals can be compared to the “Ergonomic demands, percent of workcycle” to determine the relative risk for that workstation. When all workstations have been studied in this manner, the workstations with high scores can be analyzed using an ergonomic analysis software or other conventional technique.
The theory of recording only the value for the highest stress activity in a work sequence, then applying the entire ergonomic stress time against it is based on the biomechanical model where the body working as a system, accumulates stress insults that will impinge the most stressful work component.
Conceptual workplace evaluation using an ergonomic analysis software.
This technique requires three people; a recorder, an actor and a coach. Team skills must include an ergonomic analyst, an engineer familiar with the work process, and an engineer familiar with the work measurement study. Props like a table and objects that represent parts including weight are also helpful. The actor simulates the operator motions, as described by the coach, while the recorder performs the evaluation based on observation. With the work measurement analysis already completed, the time it takes the actor to complete the motion sequence is not considered. This system works well but requires a high resource commitment. To minimize the time needed to conduct this analysis, the team must begin with an “all business attitude”. Discussion should be kept to a minimum and the players should come prepared so they are not learning the workcycle during the analysis. Typically the amount of time needed to complete this type of analysis is about 12 minutes for each 1-minute of work analyzed . Video taping the sequence is an alternative that will permit the analyst to more accurately measure body angles. Videotapes may also serve to shorten the amount of time the entire group needs to be in attendance.
Using RACECR to link the physical and virtual factories
Using ErgoSample, areas of high ergonomic stress can be found in the physical factory. By comparing the ErgoSample result with the actual reported injuries, an association of high-risk activities and injury reports can be made. When conducting an ErgoStress analysis, all areas of high-risk activity should be targets for stress reduction. Areas of risk activity that have been associated with a high ergonomic injury incident rate should be looked at more closely. The scoring systems in both ErgoSample and ErgoStress can be adjusted to improve risk visibility. See Figure 6
By stepping through this process we can perform an easy, stressful/not-stressful analysis of operator actions, note occurrences of highest stress, and then associate the evaluation with time to produce a stress profile. An analysis indicating high potential for risk can then be analyzed further using a more complex analysis system.
Figure 6 "ErgoStress Analysis in the Product Design and Development Cycle" - Omitted
The principal contribution of the RACECR system is its ability to analyze production arenas to find ergonomic problems early in the design process. The methodology and tools presented here are the instruments of change. To be truly functional in a work environment these concepts need to become a normal part of the product development process.
ErgoSample can be used independently to analyze the ergonomic quality of the current production environment, and can lead the analyst to areas for improvement.
The ErgoStress Analysis method can be applied at any point along the product development path. It can also be used to analyze an existing operation where the analyst does not have the ability to view the process directly such as may exist in remote or dark room environments.
The most important part of the process is the introduction of a method that will improve ergonomic awareness. These activities will reap benefits far beyond injury reduction. The cost of ergonomic injury is very real and the cost did not just arrive with government regulations. Business, whether in the continental U.S. or in an emerging industrial nation, are subjected to a very real economic loss when a worker is unable to perform the required tasks.
Workers are not a disposable commodity in any part of the world. Factories who do not protect their workers from ergonomic injury will continue to suffer the economic damage from those losses. Other manufacturers and service providers, who learn to effectively avoid injury, can lower production costs and become more competitive.
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Copyright 1998, Xerox Corporation