Efficient Utilization of Employees in the Garment Industry using Operations Research.

TOPIC - Efficient Utilization of Employees in the Garment Industry using Operations Research.

INTRODUCTION

Proper utilization of manpower determines the efficiency of a system. The aim is to determine a mechanism for the garment industry to utilize the manpower with highest efficiency. In a garment industry, the study was done to determine the proper mechanism for assigning employees different operations in the sewing section.

The scope is restricted to sewing section due to following considerations-:

(A)          Complex combinations of operation are done by large number of workers.

(B)          Cost of production mainly depend on this section.

SITUATION ANALYSIS

(A)          Current efficiency of employees is 50% and there is a large scope in improvement.

(B)          Selling price of the product is beyond the control of the company due to competition in garment industry.

(C)          There are 450 employees in sewing section which are grouped into 18 teams having approx. 25 employees.

(D)          Teams have number of employees according to the complexity of work.

(E)          Each employee work for 10.5 hours a day and there is 5% absenteeism on an average.

(F)          After getting the cut pieces each employee is given proper instructions and the required tools.

(G)         Time is analyzed by considering sewing time, time for handling tools, arranging and idle time which occur due to delay by previous employee.

(H)         Company currently uses GSD for average time allocation for each operation.

(I)              The experienced staffs assign operations to the employees which is a problem in reaching high efficiency.

CONSTRUCTION OF MODEL

    The decision variables used in the mathematical model of

assignment, are defined as follows:

Xij = 1                 if employee i performs task j                                   2

         0                 otherwise

tij is the time taken by the ith employee to perform the jth

task.

Then the objective function ΣΣt ijxij denotes the total

time required to produce a single product from the style.

Σxij =1 for all j = 1,2,…n                                      3      

Σ xij =1 for all i = 1,2,…m                                    4

Equation (3) states that each task to be performed by exactly

one employee and (4) states each employee is to perform

exactly one task

To minimize this two modifications are done.

(a) the concepts of integer programming have been integrated with the model in order to choose between the best set of employees

Σxij =1 for all j = 1,2,…n

Σ xij =1 for all i = 1,2,…m

Σ Xij = n

(b) It is assumed that more than one employee can be assigned to a single task. Let αj be the number of employees assigned to task j.

Accordingly the final version of the model would read as

Follows

Minimize    ΣΣt ijxij      

subject to   Σ Xij = α

SOLVING THE MODEL USING MICROSOFT EXCEL

The wok book has been designed with a capacity to include 50 employees and 33 tasks generating 1650(=50x33) variables. The high capacity requirement of the model generated can’t be solved by using the inbuilt Excel Solver. Due to this reason an Excel add-in is used to replace the Excel Solver. the generated Excel workbook requires no technical work to be done by the user. It is recommended to keep a separate workbook for each team. However the maximum number of employees that can be entered into the workbook is 50, which is around twice the number of employees that is usually allocated into a team. This has enabled the company to keep additional records of important employees. These additional records can be used to evaluate the team with different combinations of employees which can be used for efficient employee transitions between teams. The first sheet of the workbook is named “Timing”. This includes previous timing records of each and every employee in respect of styles. These timing records are obtained by calculating the time taken by a particular employee to perform a particular operation per unit of SMV In the next worksheet the final model is presented in the form of two matrices. The first matrix provides the time taken by each and every employee to complete each task defined. The second matrix contains binary values which indicate whether a given employee is assigned for a given task or not.

Whenever the user enters the details of the style to the workbook, the default values of the two matrices are automatically calculated

RESULTS

The efficiency of the company is calculated by the formula

E =( (n × TSMV ) / 60  )/PH                                                                  (13)

Where E: Efficiency

           n: Number of units produced within the day

    TSMV: Total SMV of the style

          PH: Production hours of the day.

The efficiency has increased dramatically due to application of the model developed by this study and reached to 80%. This improvement was mainly achieved by minimizing the bottlenecks by the optimal allocation of the employees.

CONCLUSION

This improvement was mainly achieved by minimizing the bottlenecks by the optimal allocation of the employees. The goal was successfully achieved by using the linear programming algorithm.

Analysis and Design of a Solar Charge Controller BY using MPPT

Analysis and Design of a Solar Charge Controller BY using MPPT

Introduction

This paper presents a new solar/battery charge controller that combines both MPPT and over-voltage controls as single control function. The converter is configured in parallel power transfer mode (PPT) to achieve higher efficiency. PWM control with maximumPower point tracking algorithm is used to extract maximum power from the PV modules In Solar Home Systems and inverter systems as well as in some PV hybrid systems solar charge controllers are the central control unit regulating the overall energy flow within the system. Therefore it is a central and critical component which has to be selected carefully. It is important to extract maximum power from PV under varying temperature and solar radiation levels. A maximum power point tracking (MPPT) device is used between the PV array and the load (typically batteries) to optimize the power transfer from the PV array to the load. Controlling the power flow by providing two paths using a parallel power transfer (PPT) technique results in reduced power loss is in the converter. The parallel power transfer approach is to split the power flowing into the load into two paths as: (1) power flowing directly to the load without the converter (Pp) and (2) power flowing to the load through the converter (Pm)

FUNCTIONS OF SOLAR CHARGE CONTROLLERS

Ø  It has to control the whole energy flow in the system

Ø  low voltage disconnection (LVD) to protect the battery from deep discharge

Ø  high voltage disconnection (HVD) to protect the battery from overcharging.

Ø  It should have a good battery state of charge calculation (SOC) in order to be able to monitor the battery status

CONTROL LAW FOR CHARGE CONTROLLER

To find a control law that regulates the battery voltage in the face of a current disturbance using classical control tools, a small signal model governing how a small change in battery current dynamically affects the battery voltage should be analyzed. For this purpose a small signal model of a lead acid battery with battery current i as control input and battery voltage Vbatt as the controlled state variable is derived. The following assumptions were made while deriving the small signal model and subsequent transfer functions:

1. Operating point is near full battery charge corresponding to a maximum allowed battery thresh-hold voltage VTH since the over-voltage controller is supposed to work close to this point as will be pointed out later.

2. Capacity change due to change in current amplitude is assumed to be small.

3. Any variations in resistance and capacitance due to SOC near operating point can be neglected.

4. Variation in load current is an external disturbance.

5. Battery current has positive polarity during charging.

SHUNT CONTROLLERS

Good solar charge controllers have a very low self consumption  (< 4 mA) and come within a robust case with big connection terminals. In addition to this good controllers have

a user friendly display indicating all system values.

Schematic of Shunt controller:

In case T1 is open, current flows through T2 to the battery. If T1 is closed the short circuit current of the module flows through T1 and no current flows to the battery. In the night T2 is open and prevents a current from the battery back to the module. T3 controls the load

 Characteristics

Shunt controllers have a very good EMC behaviour as the current changes in switching mode just between the charging current Im and the short circuit current Isc. Such  controllers have the highest charging efficiency as the current just flows through one part T2. This topology allows good protections against wrong polarity (battery and load side) and protection features against high temperature and error currents

Hot Spots

In case of partial shading of the solar module a local hot spot might appear. The voltages of the irradiated cells add up, while the shaded cell is driven in reverse voltage mode. If this cell is driven at less than -20V a pn break through could destroy this cell and the module. To prevent this all TÜV, IEC or ISPRA certified modules have suitable bypass diodes which protect the cell in case of partial shading. Normally 18 cells are protected by one diode to keep the reverse voltage below -10V. In case of partial shading the current then flows through the bypass diode. It has been reported that the use of shunt controllers effects a hot spot in solar modules. Technically this is only possible if solar modules without bypass diodes are used. Nowadays such modules do no longer exit. This means there is no limitation in using shunt controllers due to hot spot risk. Beside this more than 1 Mio shunt controllers dominate the world market and prove day by day a good compatibility with all types of solar modules

THE PROPOSED CHARGE CONTROLLER

 A schematic of the proposed charge controller where the current reference generated by the voltage control loop is dynamically limited to have an upper value equal to maximum power point current. The DC/DC converter can be thought of as a controlled current source that injects a given amount of current i into the battery depending on the amount of deviation of the battery voltage from a set thresh-hold value Vbatt ,ref. If a voltage source type load is connected at the output of a DC/DC converter, the output power can be maximized by increasing the output current [9, 10]. In this case since the load seen by the DC/DC converter is battery which is a voltage source type load, so long as there is an error between the battery voltage and thresh hold voltage set point Vbatt, ref, the reference current generated will increase significantly as a result of the over-voltage control action. The output current will, however, never exceed the maximum current due to the dynamic limitation. The PV array, therefore, will always work at MPP at battery voltages away from the over voltage thresh hold point and will automatically start shifting the PV operating point to limit the PV power produced as the voltage nears the thresh hold point (i.e. over-voltage control). The maximum power point current referred to the output (inductor) side of the DC/DC converter is dynamically calculated by the MPPT algorithm as function of the instantaneous irradiance, temperature and battery voltage. This imposes a dynamic upper limit on the current going into the battery and enables a seamless change between MPPT and overvoltage control operations realized in a single block without the need for switching between different modes or separate units. Finally, it is important to note that the voltage control loop will produce a large reference current due to the accumulation of error at normal operation under MPPT due to its integral action. To prevent wind up effect as the over-voltage control action starts, an anti-wind up is implemented to reset the integral output. It is important to point out also that as the over-voltage controller’s operating regime is only near the threshold point where the battery resistance and capacitance are not expected to change, our original assumption to neglect the independence on state of charge will not entail any error on the choice of the controller parameters.

CONCLUSION

A simplified solar/battery charge controller which combines both MPPT and over-voltage controls as single control function is proposed. A small signal model of lead acid battery, not available in literature, is also derived in detail to enable accurate design of the developed charge controller. Two case studies are conducted first to evaluate the transient and voltage overshoot response of the designed controller. Secondly, a comparative study is made based on realistic irradiance data to evaluate the performance of the proposed charge controller in terms of energy utilization factor and overvoltage compared to the conventional series hysteretic on/off controller. The designed controller is shown to have very fast transient response and very small transitory voltage overshoot. It is also found that the proposed charge controller shows better PV energy capture than the on/off controller.

INDUSTRIAL ENGINEERING APPLICATION IN COAL HANDLING PLANT

INDUSTRIAL ENGINEERING APPLICATION TO COAL HANDLING PLANT

INTRODUCTION

A coal handling plant is a facility that washes coal of soil and rock, preparing it for transport to market. It may also be called a “coal preparation plant (CPP)”, “coal handling and preparation plant” (CHPP), “prep plant,” “tipple,” or “wash plant”. Caiman coal handling plant can handles the coal from its receipt to transporting it to Boiler and store in Bunkers. It also processes the raw coal to make it suitable for Boiler Operation. It Receipt of coal from coal mines, weighing of coal, crushing it to required size and transferring the quanta of coal to various coal mill bunkers. This is the responsibility and duty of the coal handling plant and its staff.

Crushing and screening in coal handling processing

 Crushing and screening are very important step in coal handling processing:

Crushing

Crushing reduces the overall size of the ROM coal so that it can be more easily handled and processed within the coal handling plant. Crushing requirements are an important part of coal handling plant design and there are a number of different types.

Screening

Screens are used to group process particles into ranges by size. These size ranges are also called grades. Dewatering screens are used to remove water from the product. Screens can be static, or mechanically vibrated. Screen decks can be made from different materials such as high tensile steel, stainless steel, or polyethylene.

 

Equipment used in a coal handling plant

1. Pull chord switch

a series of such switches are arranged in series at a 1m distance on the side of conveyor belt. The power supply to rotor of the conveyor belt is established only if all switches in series are connected.

2. Vibrating feeder

The coal stored in a huge hub is collected on the belt through vibrations created by the vibrating feeder.

3. Flap gates

These are used to channelize the route of coal through another belt in case the former is broken or unhealthy. The flap gates open let the coal pass and if closed stop its movement.

4. Magnetic separator

these are used to separate the ferrous impurities from the coal.

5. Metal detector

These are detect the presence of any ferrous and non-ferrous metal in the coal and sends a signal to a relay which closes to seize the movement of belt until the metal is removed. It basically consists of a transmitter and a receiver.

The transmitter consists of a high frequency oscillator, which produces a oscillations of 1500 Hz at 15V. The receiver receives this frequency signal. If there is any presence of metal in the coal. Then this frequency is disturbed and a tripping signal is send to relay to stop the conveyor belt.

6. Belt weightier

1.     It is used to keep an account of the tension on the belt carrying coal and is moves accordingly to release tension on the belt.

7. Reclaim hopper

Reclaimation is a process of taking coal from the dead storage for preparation or further feeding to reclaim hoppers. This is accomplished by belt conveyors

 Availability of Coal in India.

 (1) Coking Coal.

It is used for iron and steel industry and smelting. It is found in Jharia coal mines. Ordinary coking coal is found in Raniganj and the western part of Jharia, Bokaro, Ramgarh, northern Karanpura (Damodar Valley) and in some mines of M.P

(2) Ordinary Coal.

Apart from coking coal the ordinary variety of coal has reserve of 64 billion tonnes. This type of coal is used in railway engines, steamships, thermal electric plants, chemical industry and for domestic purposes.

This type of coal is found in (i) Western Raniganj, (ii) Karanpura (Northern and Southern part), (iii) Bokaro (iv) Rajmahal (Damodar Valley) (v) Talcher (Mahanadi Valley) (vi) Singrauli, Korba, Sohagpura (vii) Sanhat (Sone Valley) (viii) Kampatee (Maharashtra) (ix) Godavari Valley (A.P)India being a large country its every state tries to get coal from the nearest source in order to cut transport charges and its early supply. As such:(i) The Northern states of India depend upon coal produced in Raniganj, Jharia, Bokaro, Karanpura, Rajmahal and Singrauli.(ii) The Southern Indian States meet their coal demand from coal of Godavari valley mines.(iii) The north-eastern states draw coal from Assam, Arunachal and Meghalaya states, situated close by.(3) Lignite Coal (Production).This poor quality coal is extracted in various parts of the country like Jammu and Kashmir, Rajasthan (Bikaner), Gujarat (Bharauch and Kutchch) and Tamil Nadu (Neyveli). Transportation of coalThere are four ways of Transportation.•      1. Railways.
•      2. Ropeways.•      3. Roadways.•      4. waterways.MODE OF TRANSPORT        Important modes of   transport  of  coal  are  Railways, Road, Merry-go-Round Systems,  Conveyor  Belts and the Rail-cum-Sea Route (Annexure-XII). The shareof these modes of transport in the total movement of coal is approximately as under:        (a) Railways   53.5%        (b) Road    17.0%        (c) MGR System   22.7%        (d) Other (Belt Conveyor          Ropeways, Rail-cum-Sea          Routes etc)     6.8%             ------------------                                    100%             ------------------

Problem Definiton

          During rainy season usually coal supplied to thermal power plants is wet. During transfer of coal from different sources such as wagon tripler  , Arial ropeway, road weigh & coal reclaimed from stack yard to bunkering or to boiler, wet coal has to pass from the system of conveyor belt, crusher, vibrating feeders and coal transfer guide i.e. chute from one conveyor to another conveyor as shown in fig.-  . In this process of coal conveying when the coal is wet it starts accumulating to the inside part of chute slowly & start blocking the coal transfer guide. As the process goes on accumulation goes on increasing & at one stage will completely block the chute. Even after this as there is no automated provision for switching of the feeding conveyor belts motor off process goes on & chute gets choke up completely till it was recognized by the local operator, or motor will gets tripped on overload. The system the need to be cleared by removing the choke up manually by deploying manpower & till then the system will not be available for the conveying usually it takes 02to 03 hours to clear the choke up.     

PROBLEM ANALYSIS

After looking at the problem the main cause of the chut choke up was the wetness of the coal which is not under our control and  the next cause is there is no alternate provision to turn off the motor when chute choke up occurs. So it was necessary to make some provision for automatic turn off the motor whenever there is a choke up situation.

   

DEVELOPING SOLUTIONS

We decided to have some modification in electrical side to make the motor turn off whenever chute choke up takes place. We made a provision of  a window with a gate opening sideways as shown in figure.  The window hole gate is connected in such a way that it will get open whenever coal accumulation starts in the chute. We connected a levered limit switch having normally closed contact and the switch having normally closed contact opens when lever gets triggered by the opening of the gate. Whenever chute choke up starts, coal starts accumulating in the hopper and pushes the window door. This triggers the limit switch and operates switch to open state from normally closed state which turns off the motor prior to the chute choke up. Electrical connection is done from local stop push button. Limit switch which has normally closed contact is taken in series with local stop push button contact as shown in the figure   

IMPLEMENTATION 

BENEFITS:

¢ Reliability of the coal handling system is increased.¢ Down time of the system is reduced.¢ Demurrage charged by Indian railways due to delay In unloading is reduced.¢ Saves manpower required for cleaning and system restoration.¢ Electrical power consumption is reduced as there is no overloading of motors.¢ Life of conveyer belts, gearbox and motor is increased by reducing frequent overloading.