SAP (PPDS) vs Aspen Plant Scheduler (SCM/MIMI)

Advanced Production Scheduling comparison

Recently Mark Rockey posted a blog about the 5 characteristics of Advanced Production Scheduling Tools.  Around the same time, I was asked by a client about the differences between SAP (PPDS) and Aspen Plant Scheduler (SCM/MIMI) and I thought this would be a good follow-up to Mark’s blog.

Here is what we at Profit Point know about some key differences between Aspen Plant Scheduler (SCM/MIMI) and SAP PPDS that was relevant to the client’s situation (I should note that we are experts in Aspen Plant Scheduler (SCM/MIMI) and have been implementing it for the last 25 years; and while we have seen several PPDS implementations, our PPSD experience involves schedulers who are recovering from PPDS and have embraced Aspen Plant Scheduler. 🙂

Regarding optimization:

  • PPDS claims to have optimization ability. We have seen this work once, but it required an expert from SAP Germany to configure it, and that was for (in our opinion) a simple optimization problem. Optimization in Aspen Plant Scheduler is highly configurable to handle from the simplest of optimizations to the most complex and intricate. We have seen enormous benefits from setting up the optimization correctly within Aspen Plant Scheduler.
  • We are not aware of any mechanism to call out to an external optimization engine from PPDS. With Aspen Plant Scheduler, if you have customer optimization mechanisms, or in-house developed optimization expertise, the tools within Aspen Plant Scheduler allow quick and easy integration to that system either via a SQL compliant database, or via flat files.
  • Nothing like M Search is available in PPDS. M Search in MIMI is a set of advanced Optimization Algorithms (including pair-wise swaps, genetic, and simulated annealing algorithms) that is used to improve schedules based upon a user configured set of performance measures, including economic factors such as: Setup costs, Production Costs and Inventory Costs.
  • We suspect that in PPDS there is no way to make a link between activities such that when you move one activity, the other moves with it. This is a standard feature of Aspen Plant Scheduler that our schedulers love.

Regarding facilities:
We suspect that PPDS is strongly tied to the work centers as they are defined in SAP. We suspect there is no ability to model facilities that are not in the SAP master data, which you probably do today. These facilities might include manufacturing equipment that are not in the routing, but are important to the plant operations; Load racks, unloading racks, or loading docks for bulk/packaged loading/unloading; labor resources for labor constrained operations. In Aspen Plant Scheduler, you have options. You do not need to rely on the work-centers as they are defined in SAP. Additional resources can easily be added and other (non-costed) equipment can be modelled. For instance, auxiliary equipment that is shared by several reactors can be set-up and scheduled showing the scheduler the constraints caused by these shared facilities.

Regarding other master data:
From what we’ve seen of PPDS, the data source is exclusively SAP, and thus it will use standard cycle times, set-up times, and other standard data that was created for financial accounting purposes, and may not be suitable for detailed scheduling purposes. We know that we routinely use Aspen Plant Scheduler based data (plant engineer based data) for the following: cycle times, set-up time, clean Times, sequence dependent cleans, count dependent cleans, quantities to account for scrap and recycle loops, and loading date & time. We routinely use these more accurate and precise values than what is available in SAP because the schedule is made more believable because of it. SAP data is often good enough for costing, but not good enough for high fidelity scheduling.

Regarding programming language:
PPDS has nothing available like Aspen Plant Scheduler’s programming language (MIMI/e) and the ability to generate:

  • Custom scheduling methods and algorithms to increase throughput in a realistic way.
  • Custom reports that leverage the Aspen Plan Scheduler’s data structures like PATHX (material flow and their linkages), PROSLI (projected inventory by product in time slices), and JITB (Just In Time Bound for an activity) to name a few.
  • Custom planning board actions that highlight or resolve issues.

What is the value to you for having high fidelity schedules that the operations folks believe and thus follow? We have seen that unrealistic schedules erode the usefulness of having a scheduling tool, causing the operations folks to do it themselves. We have seen this erosion spawn Excel based replacements for scheduling run by operations when the schedule becomes sufficiently untrustworthy.

What is the value to customer service from having the scheduler have the ability to find a specific order, change the schedule to expedite that order, understand the global impact of that change, and know that the schedule will be followed?

There is nothing like Aspen Plant Scheduler’s level of external integration ( connect to any ODBC compliant database with MIMI/SQL) in PPDS that would allow you to roll your own reports and send them to a database for wide spread access. While you can request custom reports via your company’s SAP BASIS team, this is not equivalent.

We have seen PPDS work fine for small plants with simple equipment layouts. However, large or even moderately sized plants usually have not been able to make PPDS work for them. In large part, this is due to the real operating constraints that cause the simplified accounting based data to diverge from what is actually achievable in the plant. We have seen that the use of realistic data for cycle times for example, in a tool that appropriately models the real degrees of freedom that the equipment allows, contributes to a more realistic schedule. This more realistic schedule allows for significantly higher throughput and higher customer service levels.

At Profit Point, we would be happy to discuss the pros and cons of various Advanced Production Scheduling Tools with you. We will give you the facts as we know them based on your business requirements so that you can make the best decision for your company and business.

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About Jim Piermarini

Jim has extensive experience in the chemical industry, including ten years working in a plant and twenty additional years working with businesses to improve their supply chains.

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