In manufacturing environment, companies use an automated setup of tanks and hoist for chemical cleaning and coating processes. In this setup, various chemicals kept in tanks situated on a straight line and a hoist moves jobs between tanks according to job operation time and sequence. This setup is costly and can be a bottleneck process for the company. An optimized scheduling of job operations can increase throughput significantly and hence revenue for the company. This job scheduling problem is known as “Hoist scheduling Problem (HSP)” in operations research area.
We have built a mixed integer programming solution for a single hoist scheduling problem (S-HSP) with following constraints:
- Single hoist that moves to and fro on a straight track between loading and unloading stations
- Tanks on a straight line with multiple tanks available for bottleneck operations
- Heterogeneous jobs with multiple routes
- Minimum and maximum operation time for each job and tank combination
- Jobs can skip tanks based on their operation sequence
- Limited number of hangers to load jobs
The problem was solved efficiently with CPLEX. In this case, we set the model up as an integer program. But, CPLEX has the ability to solve this using constraint programming (which has been shown to efficiently solve complex scheduling problems).