Presentation on theme: "Manual Work & Worker-Machine Systems"— Presentation transcript:
1 Manual Work & Worker-Machine Systems Sections:Manual Work SystemsWorker-Machine SystemsAutomated Work SystemsDetermining Worker and Machine RequirementsMachine ClustersChapter 2
2 Three Categories of Work Systems Manual work systemWorker performing one or more tasks without the aid of powered toolsWorker-machine systemHuman worker operates powered equipmentAutomated work systemProcess performed without the direct participation of a human worker
6 Some Definitions Workpiece being machined (production work) Work unit – the object that is processed by the work systemWorkpiece being machined (production work)Material being moved (logistics work)Customer in a store (service work)Product being designed (knowledge work)Unit operations – tasks and processes that are treated as being independent of other work activities
7 Manual Work SystemsHuman body accomplishing some physical task without an external source of powerWith or without hand toolsWhen hand tools are used, the power to operate them is derived from the strength of a human workerOther human faculties are required, such as hand-eye coordination and mental effort
8 Pure Manual WorkInvolves the physical and mental capabilities of the human worker, and no machines, tools, or other implements are employed in performing the task.Material handler moving cartons in a warehouseWorkers loading furniture into a moving van without the use of dolliesDealer at a casino table dealing cardsOffice worker filing documentsAssembly worker snap-fitting two parts together
9 Manual Work with Hand Tools Manual tasks are commonly improved by the use of hand tools. A tool is a device or implement for making changes to some object (e.g., the work unit), such as cutting, grinding, striking, squeezing, or other process. A hand tool is a small tool that is operated by the strength and skill of the human user. Examples of manual tasks involving the use of hand tools include the following:Machinist filing a partAssembly worker using screwdriverPainter using paintbrush to paint door trimQC inspector using micrometer to measure a shaft diameter
10 Repetitive vs. Nonrepetitive Tasks Relatively short duration (usually a few minutes or less)High degree of similarity from one cycle to the nextNonrepetitive TaskTakes a long timeWork cycles are not similar
11 Cycle Time VariationsA main objective in work design is to determine the one best method for a task, and then to standardize its useOnce the method has been standardized, the actual time to perform the task is a variable because of:Differences in worker performancedifferences in hand and body motionsMistakes by workerVariations in starting work unitsThe learning curve phenomenonDifferences in the physical and cognitive attributes among workers performing the taskVariations in the methods used by different workers to perform the task
12 Worker Performance Defined as the pace or relative speed of working As worker performance increases, cycle time decreasesFrom the employer’s viewpoint, it is desirable for worker performance to be highWhat is a reasonable pace to expect from a worker?
13 Normal PerformanceA pace of working that can be maintained by a properly trained average worker throughout an entire work shift without injurious effect on the worker’s health or physical well-beingThe work shift is usually 8 hours, during which periodic rest breaks are allowedNormal performance = 100% performanceCommon benchmark of normal performance:Walking at 3 miles/hr
14 Normal TimeThe time to complete a task when working at normal performanceActual time to perform the cycle depends on worker performanceTc = Tn / Pwwhere Tc = cycle time, Tn = normal time, and Pw = worker performance or pace
15 Example: Normal Performance Given: A man walks in the early morning for health and fitness. His usual route is 1.85 miles. A typical time is 30 min. The benchmark of normal performance = 3 miles/hr.Determine: (a) how long the route would take at normal performance and (b) the man’s performance when he completes the route in 30 min.
16 Example: Solution (a) At 3 miles/hr, time = 1.85 miles / 3 miles/hr = hr = 37 min(b) Rearranging equation, Pw = Tn / TcPw = 37 min / 30 min = = %Alternative approach in (b):Using velocity = 1.85 miles / 0.5 hr = 3.7 miles/hrPw = 3.7 miles/hr / 3.0 miles/hr = %
17 Standard PerformanceSame as normal performance, but acknowledges that periodic rest breaks must be taken by the workerPeriodic rest breaks are allowed during the work shiftFederal law requires employer to pay the worker during these breaksOther interruptions and delays also occur during the shift
18 PFD Allowance Bathroom breaks, personal phone calls To account for the delays due to:Personal time (P)Bathroom breaks, personal phone callsFatigue (F)Rest breaks are intended to deal with fatigueDelays (D)Interruptions, equipment breakdowns
19 Standard TimeDefined as the normal time but with an allowance added in to account for losses due to personal time, fatigue, and delaysTstd = Tn (1 + Apfd)where Tstd = standard time, Tn = normal time, and Apfd = PFD allowance factorAlso called the allowed time
20 Irregular Work Elements Elements that are performed with a frequency of less than once per cycleExamples:periodic changing of tools (e.g., changing a knife blade)Irregular elements are prorated into the regular cycle according to their frequency
21 Example: Determining Standard Time Given: The normal time to perform the regular work cycle is 3.23 min. In addition, an irregular work element with a normal time = 1.25 min is performed every 5 cycles. The PFD allowance factor is 15%.Determine (a) the standard time and (b) the number of work units produced during an 8-hr shift if the worker's pace is consistent with standard performance.
25 Standard Hours and Worker Efficiency Two common measures of worker productivity used in industry to assess a worker’s productivity are standard hours and worker efficiencyStandard hours – represents the amount of work actually accomplishedHstd = Q TstdHstd = standard hours accomplished; Q = quantity of work units completed; Tstd = standard time per work unitWorker efficiency – work accomplished as a proportion of shift hoursEw = Hstd / HshEw = worker efficiency; Hstd = # of standard hours of work accomplished; Hsh = # of shift hours (8 hr)
28 Worker efficiencyWorker efficiency is commonly used to evaluate workers in industry.In many incentive wage payment plans, the worker’s earnings are based on his or her efficiency or the number of standard hours accomplished.Worker efficiency and standard hours are easily computed, because the number of hours in the shift and the standard time are known, and the number of work units produced can be readily counted.
29 Worker-Machine Systems When worker operates a powered equipment we refer to the arrangement as a worker-machine system.Examples:Machinist operating a milling machineFactory worker loading and unloading parts at a machine tool.Truck driver driving an 18-wheel tractor-trailerWorker crew operating a rolling mill that converts hot steel blocks into flat plates.Clerical worker entering data into a PC
30 Types of Powered Equipment Distinguished from hand tools by the fact that a source of power other than human strength is used to operate it. Common power sources are electric, pneumatic, hydraulic, and fossil fuel motorsPortable power tools are light enough in weightportable power drills, rotary saws, chain saws, and electric hedge trimmers.Mobile powered equipment are generally heavy pieces of equipmentTransportation equipment, agricultural and lawn-keeping, forklift trucks, electric power generator at construction siteStationary powered machines stand on the floor or ground and cannot be moved while they are operatingMachine tools (e.g., turning, drilling, milling); office equipment (personal computers, photocopiers, telephones, fax machines); cash registers, heat treatment furnaces
32 Numbers of Workers and Machines Means of classifying worker-machine systems is according to whether there are one or more workers and one or more machinesOne worker andOne machineTaxicab driver and taxiOne worker & Multiple machinesA worker tending several production machinesMultiple workers andOne machineShip's crewMultiple workers andMultiple machinesEmergency repair crew responding to machine breakdowns in a factory
33 One Worker and One Machine Good work design attempts to achieve the following objectives:Design the controls of the machine to be logical and easy to operate for the worker.Design the work sequence so that as much of the worker’s task as possible can be accomplished while the machine is operating, thereby minimizing worker idle time.Minimize the idle times of both the worker and the machine.Design the task and the machine to be safe for the worker.
34 Level of Operator Attention Full-time attentionWelders performing arc weldingPart-time attention during each work cycleWorker loading and unloading a production machine on semi-automatic cyclePeriodic attention with regular servicingCrane operator in steel millPeriodic attention with random servicingFirefighters responding to alarms
35 Two welders performing arc welding on pipe - requires full-time attention of workers (photo courtesy of Lincoln Electric Co.)
36 Cycle Time Analysis in Worker Machine System In terms of cycle time analysis, worker-machine systems fall into two categories:systems in which the machine time depends on operator control, the task can be either repetitive or nonrepetitivesystems in which the machine time is constant and independent of operator control, and the work cycle is repetitive.
37 Cycle Time with no Overlap between Worker and Machine If there is no overlap in work elements between the worker and the machine, then the normal time for the cycle is simply the sum of their respective normal times:Normal time for cycleTn = Tnw + TmWhere Tnw = normal time for the worker-controlled portion of the cycle, min: and Tm = machine cycle time (assumed constant).Standard time for cycleTstd = Tnw (1 + Apfd) + Tm (1 + Am)where Tnw = normal time of the worker, min; Tm = constant time for the machine cycle, min; Am = machine allowance factor, used in the equation as a decimal fraction
41 Worker-Machine Systems with Internal Work Elements In the operation of a worker-machine system, it is important to distinguish between the operator’s work elements that are performed in succession with the machine’s work elements and those that are performed simultaneously with the machine elements.Operator elements that are performed sequentially are called external work elements while those that are performed simultaneously with the machine cycle are called internal work elements.
42 Example 2.10 Internal Versus External Work Elements in Cycle Time Analysis The work cycle in a worker-machine system consists of the elements and associated times given in the table below.All of the operator’s work elements are external to the machine time.Can some of the worker’s elements be made internal to the machine cycle, and if so, what is the expected cycle time for the operation?
45 CommentAlthough the total times for the worker and the machine are the same as before, element 4 in the revised cycle (which Consists of elements 1, 2, and 6 from the original work cycle) is performed simultaneously with the machine time, resulting in the following new cycle time:Tc = = 0.97 minThis represents a 34% reduction in cycle time, which translates into a 53% increase in production rate.When internal elements are present in the work cycle, it must then be determined whether the machine cycle time or the sum of the worker’s internal elements take longer.
46 Automated Work Systems Automation is the technology by which a process or procedure is accomplished without human assistanceImplemented using a program of instructions combined with a control system that executes the instructionsPower is required to drive the process and operate the control system
47 Levels of Automated Systems Semiautomated machinePerforms a portion of the work cycle under some form of program controlHuman worker tends the machine for the remainder of the cycle, by loading and unloading itOperator must be present every cycleFully automated machineOperates for extended periods of time with no human attention
48 Automated robotic spot welding cell (photo courtesy of Ford Motor Company)