APS has the same capacity model for long term and short term planning, and the same precise planning and scheduling based on precise process data (if available). For example, APS releases a "grand scheduling" plan that is accurate to each resource for three months, and then cuts out monthly plans, weekly plans, and daily plans. In fact, the long-term production plan of the factory is based on the factory capacity, and the short-term production plan of the workshop is based on the workshop capacity. For mass production, the gap between factory capacity, workshop capacity and resource capacity is not large, but in discrete manufacturing enterprises, the formulation models of long-term plans, medium-term plans and short-term plans are different.

Therefore, at present, APS is rarely used for planning in practical applications of factories with large discretization. In most instances APS is a plug-in for local scheduling. Over the years, factories have moved from high-volume production to low-volume production. Most of them still apply the mass production planning mindset. For enterprises with sufficient orders, quarterly plans, monthly plans and weekly plans are designed in accordance with 100% of production capacity. In fact, the production site will be subject to a lot of interference, insert and withdraw orders, equipment personnel exceptions will affect the production capacity. Therefore, the implementation rate of medium - and long-term production plans is reduced, which makes some orders delayed, idle and waiting for materials, overtime and so on.

The reason why the plan does not work well

In mass production mode, production planning is easy to do and the effect will be good. The principle of its planning is to import the product tasks ready for production into the system, including routing and the ability of each device resource into the system, and run under the limited resource capability model, equivalent to virtual production. This results in a detailed daily and hourly plan. Then cut out the daily plan can be used to make work orders, cut out the weekly plan, monthly plan for production preparation or material procurement. APS is a scheduling tool, and it makes no difference between scheduling and calculating scheduling capacity models. The input is the order, the production process flow, and the output is the production instruction. If the monthly plan, it can be accurate to a month later a certain device at a certain minute to do what. As long as it is a plan, there are uncertainties, errors are normal. It would be nice if the daily plan's error could be measured in hours. The minutes and seconds in the instructions are meaningless. It is very good that the error of the weekly plan can be half a day, and the information of the machine in the instruction is meaningless. If it is a monthly plan, the error is three or two days is normal. Since most instructions are issued to people, people can correct errors in instructions, so these errors can be tolerated. If it's a commanding robot, then there can be no error.

The order of mass production can be obtained through market prediction, the product is relatively mature, the basic data of the input are basically ready, and even the product data to be produced after half a year are complete. The MRP of ERP can be used to make the material requirement plan, and after manual adjustment, the factory procurement plan, production plan, financial plan and so on can be obtained. However, in the case of small-batch and multi-variety customization, the order information is incomplete and inaccurate in the preparation of the plan. The closer to the production time, the better the information. For many orders, detailed process documentation is prepared before production begins. As a factory, it is impossible not to make production plans. However, without detailed process data and resource data, APS cannot make plans. By the time it's complete, it's long past the time to plan. In such a scenario, the planning function of APS is far less practical than that of MRP.

As a scheduling tool, the challenge is to make scheduling instructions close to the habits of shop schedulers, team leaders, and workers. If your scheduling results are not in line with their habits, naturally there will be questions and conflicts, and the manual will not feel good. Since the scheduling instruction is the decision of the workshop, it involves the rights, responsibilities and obligations of some employees. APS needs to take these issues into account, and if there are too many conflict of interest problems like this, APS will be difficult to implement in the workshop. In fact, the habits of workshop employees are also a kind of experience, including industrial knowledge. APS should also learn from this. For example, a machining center has several machine tools. After the workshop receives a batch of work orders, it usually gives which machine or several machine tools to assign this batch of work according to the habit. If the APS is configured by itself, it must be assigned according to certain rules. If the rules are different from the habits of the workers in the work center, the schedule cannot be performed. Because the habits of workers include experience and knowledge, they will find your schedule incomprehensible and irregular.