Work Systems and How They Work Chapters: • Manual Work and Worker-Machine Systems • Work Flow and Batch Processing • Manual Assembly Lines • Logistics Operations • Service Operations and Office Work • Projects and Project Management Part I
Manual Work & Worker-Machine Systems Sections: • Manual Work Systems • Worker-Machine Systems • Automated Work Systems • Determining Worker and Machine Requirements • Machine Clusters Chapter 2
Three Categories of Work Systems • Manual work system • Worker performs one or more tasks without the aid of powered tools (e.g. hammers, screwdrivers, shovels) • Worker-machine system • Human worker operates powered equipment (e.g. a machine tool) • Physical effort (less) • Machine power(more) • Automated work system • Process performed without the direct participation of a human worker
Some Definitions • Work unit – the object that is processed by the work system • Workpiece being machined (production work) • Material being moved (logistics work) • Customer in a store (service work) • Product being designed (knowledge work)
Manual Work Systems • Most basic form of work in which human body is used to accomplish some physical task without an external source of power • With or without hand tools • Even if hand tools are used, the power to operate them is derived from the strength and stamina القدرة على التحمل of a human worker • Hairbrush vs hair dryer • Of course other human faculties قدرات بشريةare also required, such as hand-eye coordination and mental effort
Pure Manual Work Involves only the physical and mental capabilities of the human worker without machines or tools. • Material handler moving cartons in a warehouse • Workers loading furniture into a moving van without the use of dollies • Office worker filing documents • Assembly worker snap-fitting two parts together
Manual Work with Hand Tools • Manual tasks are commonly augmented by تعزز بuse of hand tools. • Tool is a device for making changes to objects (formally work units) such as cutting, grinding,striking, squeezing • Scissor, screwdriver, shovel • Tools can also be used for measurement and/or analysis purposes • Workholder to grasp or poisiton work units
Manual Work with Hand Tools Examples: • Machinist filing a part • Assembly worker using screwdriver • Painter using paintbrush to paint door trim • QC inspector using micrometer to measure the diameter of a shaft • Material handling worker using a dolly to move furniture • Office worker writing with a pen
Cycle Time Analysis • Cycle time Tc where Tek= time of work element k, where k is used to identify the work elements (min) ne = number of work elements into which a cycle is divided.
Example 2.1: A repetitive Manual Task • Current method: An assembly worker performs a repetitive task consisting of inserting 8 pegs أوتاد into 8 holes in a board. A slightly interference fit is involved in each insertion. The worker holds the board in one hand and picks up the pegs from a tray with other hand and inserts them into the holes, one peg at a time.
Example 2.1: A repetitive Manual Task • Current method and current layout:
Example 2.1: A repetitive Manual Task • Improved method and improved layout: • Use a work-holding device to hold and position the board while the worker uses both hands simultaneously to insert pegs. • Instead of picking one peg at a time, each hand will grab أمسك بfour pegs to minimize the number of times the worker’s hands must reach the trays.
Example 2.1: A repetitive Manual Task • Improved method • The cycle time is reduced from 0.62 min to 0.37 min. • % cycle time reduction=(CTcurrent-CTimproved)/CTcurrent =(0.62-0.37)/0.62=40%
Example 2.1: A repetitive Manual Task • Production ratecurrent=1/0.62 min=1.61 units per min (throughput) • Production rateimproved=1/0.37 min=2.70 units per min • % increase in R=(Rimproved-Rcurrent)/Rcurrent =(1.61-2.70)/1.61=68% • It is important to design the work cycle so as to minimize the time required to perform it. • Of course there are many alterantive ways to perform a given task. Our focus is on the best one.
One Best Method Principle • Of all the possible methods that can be used to perform a given task, there is one optimal method that minimizes the time and effort required to accomplish it • Attributed to Frank Gilbreth • A primary objective in work design is to determine the one best method for a task, and then to standardize it • This one best refers to an average worker with a moderate level of skill, operating under normal working conditions with nominal material quality and tool/equipment availability
Cycle Time Variations • Once the method has been standardized, the actual time to perform the task is a variable because of: • Differences in worker performance • Mistakes, failures and errors • Variations in starting work units • Variations in hand and body motions • Extra elements not performed every cycle • Differences among workers • The learning curve phenomenon
Worker Performance • Defined as the pace (tempo) or relative speed with which the worker does the task. • هى الوتيرة (الإيقاع)، أو السرعة النسبية التي يؤدى بها العامل المهمة. • As worker performance increases, cycle time decreases • From the employer’s viewpoint وجهة نظر صاحب العمل, it is desirable for worker performance to be high • What is a reasonable performance/pace to expect from a worker in accomplishing a given task?
Normal Performance (pace) الأداء العادي • A pace of working that can be maintained by a properly trained average worker throughout an entire work shift without harmful short-term or long-term effects on the worker’s health or physical well-being • The work shift is usually 8 hours, during which periodic rest breaks are allowed • Normal performance = 100% performance • Faster pace > 100%, slower pace < 100% • Common benchmark of normal performance: • Walking at 3 mi/hr (~4.83 km/hr)
Normal Time • The time to complete a task when working at normal performance (Tn ) • Actual time to perform the cycle depends on worker performance Tc = Tn / Pw where Tc = cycle time, Tn = normal time, Pw = worker performance or pace
Example 2.2: Normal Performance • Given: A man walks in the early morning for health and fitness. His usual route is 1.85 miles. The benchmark of normal performance = 3 mi/hr. • Determine: (a) how long the route would take at normal performance (b) the man’s performance when he completes the route in 30 min.
Example 2.2: Solution (a) At 3 mi/hr, normal time = 1.85 mi / 3 mi/hr = 0.6167 hr = 37 min (b) Rearranging equation, Pw = Tn / Tc Pw = 37 min / 30 min = 1.233 = 123.3 % • If worker performance > 100%, then the time required to complete the cycle will be less than normal time. • If worker performance < 100%, then the time required to complete the cycle will be greater than normal time.
Standard Performance • Same as normal performance, but acknowledges يقر that periodic rest breaks must be taken by the worker • Periodic rest breaks are allowed during the work shift • Lunch breaks (1/2 or 1 hour) • usually not counted as part of work shifts • Shorter rest beraks (15 mins) • usually counted as part of work shifts
Rest Breaks in a Work Shift • A typical work shift is 8 hours (8:00 A.M. to 5:00 P.M. with one hour lunch break) • In Turkey work time is defined as 45 hours a week (so 8:00 A.M. to 6:00 P.M. with one hour lunch break, provided that workers work for 5 days) • The shift usually includes one rest break in the morning and another in the afternoon. • The employers allows these breaks, because they know that the overall productivity of a worker is higher if rest breaks are allowed. • In Turkey the rest periods are not included in daily work hours in which employersare paid for.
Standard Performance • Of course other interruptions and delays also occur during the shift • Machine breakdowns • Receiving instructions from the foreman • Telephone calls • Bathroom/toilette breaks etc.
Personal time, Fatigue, Delay (PFD) Allowance • To account for the delays and rest breaks, an allowance is added to the normal time in order to determine allowed time for the worker to perform the task throughout a shift • Personal time (P) • Bathroom breaks, personal phone calls • Fatigue (F) تعب • Rest breaks are intended to deal with fatigue • Delays (D) • Interruptions, equipment breakdowns
Standard Time • Defined as the normal time but with an allowance added into account for losses due to personal time, fatigue, and delays Tstd = Tn (1 + Apfd) where Tstd = standard time, Tn = normal time, Apfd = PFD allowance factor • Also called the allowed time • Now we are confident to say that a worker working at 100% performance during 8 hours can accomplish a task of 8 hour standard time.
Irregular Work Elements • Elements that are performed with a frequency of less than once per cycle • Examples: • Changing a tool • Exchanging parts when containers become full • Irregular elements are prorated into the regular cycle according to their frequency
Example 2.3: Determining Standard Time and Standard Output • 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 (b) the number of work units produced during an 8-hr shift if the worker's pace is consistent with بما يتفق مع standard performance.
Example 2.3: Solution • Normal time of a task involves normal times for regular and irregular work elements • Normal time Tn = 3.23 + 1.25/5 = 3.48 min Standard time Tstd = 3.48 (1 + 0.15) = 4.00 min (b) Number of work units produced during an 8-hr shift Qstd = Hsh/ Tstd Qstd = 8.0(60)/4.00 = 120 work units Hsh=number of shift hours, hr
Example 2.4: Determining Lost Time due to the Allowance Factor • Given: An allowance factor of 15% is used. • Determine the anticipated amount of time lost per 8-hour shift. • Solution: Hsh=(Actual time worked)(1+ Apfd) 8.0 hour =(actual time worked) (1+0.15) Actual time worked = 8/ 1.15 = 6.956 hr Time lost = Hsh– Actual time worked Time lost = 8.0 – 6.956 = 1.044 hr
Example 2.5: Production rate when worker performance exceeds 100% • Given: From Ex. 2.3,Tstd = 4.00 min and Tn = 3.48 min. The worker’s average performance during an 8-hour shift is 125% and the hours actually worked is 6.956 hr (which corresponds to the 15% allowance factor). • Determine daily production rate.
Example 2.5: Solution • Based on normal time Tn = 3.48 min, the actual cycle time with a worker performance of 125%, Tc =3.48 / 1.25 = 2.78 min. (see slide 23) • Assuming one work unit is produced each cycle, the corresponding daily production rate, Rp = 6.956 (60) / 2.78 =150 work units OR • 125% of 120 units (we know that from Ex. 2.3.b) at 100% performance = 150 units
Standard Hours and Worker Efficiency • Two (three) common measures of worker productivity used in industry • Standard hours – represents the amount of work actually accomplished during a given period (shift, week) • Quantity of work units (in terms of time) produced Hstd = Q Tstd where Hstd =standard hours accomplished, hr Q= quantity of work units completed during the period, pc Tstd=standard time per work unit, hr/pc • Worker efficiency – work accomplished during the shift expressed as a proportion of shift hours Ew = Hstd / Hsh Ew=worker efficiency, % Hsh=number of shift hours, hr
Example 2.6: Standard hours and worker efficiency • Given: The worker performance of 125% in the previous example. Example 2.5 • Determine: (a) number of standard hours produced (b) worker efficiency • Solution: (a) Hstd = Q Tstd Hstd=150(4 min)=600 min= 10.0 hr (b) Ew = Hstd / Hsh Ew= 10hr / 8 hr =125 %
Example 2.7: Standard hours and worker efficiency as affected by hours actually worked • Given: The worker performance of 125%, actual hours worked is 7.42 hr. Tc = 2.78min and Tstd =4 min • Determine: (a) number of pieces produced, (b) number of standard hours accomplished, (c) the worker’s efficiency • Solution: (a) Q =Actual time worked / cycle time Q =7.42 (60) / 2.78 = 160 units (b) Hstd = Q Tstd =160 (4 min) = 640 min = 10.67 hr (c) Ew = 10.67hr / 8 hr =133.3 %