New expression of scheduling performance measures

The conventional expression of performance measures in the scheduling area has, from the very beginning, never been changed. The main characteristic of this expression is that all the jobs are considered in an overall way without considering the individual needs of specific jobs. The second drawback is lack of useful information about control. When shop floor supervisors face the situation of a delay in an operation in a schedule, the degree of deviation from the objective value cannot be derived easily. In this paper, we propose a new expression of scheduling performance measures. The new expression includes protected operations and their allowable floats. According to the new expression, we develop an algorithm to derive total float and free float for each operation in a schedule. These floats, for tackling the above problems, provide shop floor supervisors with information about how critical each operation is in a schedule, so that a suitable control action can be applied to each operation. Therefore, by resorting to rescheduling, supervisors can make every effort to reach the scheduling objective value of the original schedule.