Objective of the work

The work aims to:

Find the minimum number of labor required to meet the demand for labor in a continuous manufacturing system, which includes different hierarchical labor skills.
Provid the tour-schedule during a week, which specifies the on-off days and the assigned tasks to each labor in the system.

Defination

Manpower scheduling problem is defined as “the problem of optimally matching available labor resources to the needs for labor of an organization considering all applicable constraints”.
Manpower scheduling, workforce scheduling, employee timetabling, staff scheduling, and crew-rostering are different names for the same problem.
The workforce scheduling problem is classified as NP-complete, which can not be solved in polynomial time but whether a given solution is right can be checked in polynomial.

Application of manpower scheduling problems

This problem arises in any organization, which has a human resource , such as;

• Scheduling nurses in hospitals,

• Operators in telephone companies,

• Aircrew at airline stations,

• Patrol persons in police departments,

• Workforce at fast food restaurants, and

• Labor in manufacturing systems.

Constraints of the problem

The followings are some common constraints which appear in the workforce scheduling problems.

1- Workforce requirement; Workforce requirement determines the needed number of labor for each day and planning period during the cycle.

2- Conflict; An employee can not be assigned to more than one task in the same shift. In addition, an employee can not be assigned to two shifts that are in conflict with each other.

3- Ability; Each employee has his qualifications and personnel skills that enable him to do or not to do certain types of tasks.

Constraints of the problems

4- Work load; Employees can have different number of working hours. The aim of the schedule is to reach an equal number of working hours for each employee.

5- Individual preferences; There are different personal preferences of each employee, which restrict him to be assigned only to subsets of shifts or restrict him to the days he wants to have off.

6- Sequence of shifts; There are some sequence of shifts are not allowed such as working in two shift the rest period between them is less than certain limit ( 16 hrs).

7- Work and rest periods; The most common rest period is two days per week that may be consecutive or not.

Stages of the manpower scheduling problem

Workforce-scheduling problem solving can be done on four stages:

1-Determining the quantity of work to be done; The goal of that task is to predict the characteristics of the system transactions that change over time.

2-Determining the staffing required to do the work for each time period; Calculation of the number and skill levels of labor needed to meet the demand throughout a planning cycle.

Stages of the manpower scheduling problem

3- Developing a workforce schedule; The schedule should supplies sufficient staffing while also accounting for employee requirement.

4- Controlling and administering the schedule as the work unfolds; This task involves the real-time control of the schedule. Also, this task exhibits the ability of the schedule to meet changes occurred in the system.

Problem of interest

•The problem of inertest is scheduling hierarchical labor to tasks in continuous systems which operates for three daily shifts through the seven weekly days.

•The problem starts from determining a sufficient workforce size to meet the demand, then scheduling days on and off, and finally assigning labor to tasks.

Assumptions

We assume the following:

The system operates seven days per week.
There are three shifts per day; day-shift (D), evening-shift (E), and night-shift (N). The week-end days are the last two days.
Each shift is composed of a number of tasks. Each task requires a number of labor with different capabilities.
Each labor will work five shifts per week.

Assumptions

Each labor will have two days off per week, not necessarily to be consecutive.
The system contains different types of labor, classified hierarchically by their capabilities or experiences. A higher qualified labor can substitute a lower qualified one but not vice versa.
The schedule is rotating and is done for one week.
No employee absenteeism.

The proposed knowledge-based system (KBS)

We establish a knowledge-based system to solve the manpower scheduling problem with the same predescribed conditions.
The system is built using Visual Prolog V5.2.
The obtained schedule satisfies all the applicable constraints.

Steps of the KBS

Step 1

Feeding the system with the input data:

The input data is the tasks requirements from each labor type for each shift.
These requirements are summed to form the shift requirements from each labor type.

Steps of the KBS

Step 2

Building the facts of the system:

The input data of the problem is transformed to facts.
There are other facts that represent the status of the labor for each shift (on- off), the summation of his working shifts, shifts that contain surplus labor… etc.

Steps of the KBS

Step 3

Running the rules of the system:

This step is the proposed algorithm which starts with calculating the workforce size, then assigns on-off shifts and a specific task simultaneously to each labor.
In each assignment iteration, the system searches for a suitable labor which has the minimum workload and assign him a task to do. So, we gurantte that the workload is distributed uniformly among the available labor.
After obtaining the weekly schedule the system distributes the surplus labor on shifts in even manner.

Steps of the KBS

Step 4

Printing results:

Results are printed in a tabular format showing the required number from each labor type, the on-off shift schedule including the task assignment for each employee.
The table below shows the tour schedule obtained from the KBS

	Day
Labor	1	2	3	4	5	6	7
1	D/1	E/2	E/4	N/3	--	D/4	--
2	D/3	E/2	N/1	N/4	--	E/1	--
3	D/3	E/3	N/2	--	D/1	E/2	--
4	D/4	E/4	N/2	--	D/2	E/3	--

Advantages of the proposed KBS

The resulted number of labor from applying the KBS is equal to that of the integer-programming model. This means that we reach the optimum solution.
The KBS has the advantage of distributing the surplus workdays evenly among days and labor.

Conclusion

In this work, we presented a knowledge-based system built using Visual Prolog V5.2 to solve the tour-scheduling problem in continuous-operating facilities which include hierarchical workforce.

The proposed method is very efficient since its results are the same as integer-programming models.