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

Manual Work System

Worker-Machine System

Automated System

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

Repetitive vs. Nonrepetitive Tasks Work cycle takes a long time Work cycles are not similar Work cycle is relatively short (usually a few minutes or less) High degree of similarity from one cycle to the next In either case, the task can be divided into work elements that consist of logical groupings of motions

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 ب four 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 Differences in worker performance 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 employers are 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 = 2.78 min 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 %