Discrete process emulation system finds equipment, cycle constraints

A utomated material handling systems (AMHS) are an important component of many discrete manufacturing processes. These systems move materials from one workstation to another where processes are performed. Each process step has a unique function that requires resources and time to complete.

Cycle times for each step are often hard to synchronize; one process may require three seconds to perform and the next may require 60 seconds. Randomness is also introduced by errors, which require operator intervention to correct, and which can potentially cause time delays.

Simulating these operations provides numerous benefits including identification of:

• Potential bottlenecks where more equipment is needed;

• Excess capacity where equipment can be reduced;

• Flow control issues; and

• Errors in control logic.

Emulation adds benefits

Emulation provides benefits of simulation plus the ability to visualize system operation. At this level personnel involved in system design, layout, and production planning can experiment to optimize overall system performance. System emulation is often overlooked as contributing limited value, but if performed early in the design cycle can reduce rework of the control system and the physical operation. In addition, if maintained, it offers a means to provide system-specific training to operators, including demonstration of effects of system failures or operator errors with no production losses.

AutoMod from AutoSimulations (division of Brooks Automation, Bountiful, Ut.) is a 3D-simulation package designed to model, analyze, and develop discrete event systems, including automated material handling systems. Models are constructed using parameterized systems such as conveyors, pathmovers, automated storage and retrieval systems, and other functions.

Model development occurs in a 2-D environment, which functions similar to a standard computer-aided drafting (CAD) display. Here, the user selects types of objects to be placed, where to place them, and how to interconnect them. For example, objects can include conveyor pieces, loaders, unloaders, photoeyes, and limit switches.

Once the physical function and layout are completed, the user can define dynamic properties for all objects. Property definition is performed using simple menus that allow for rates, hold times, and capacities. Important classes of properties are upset condition options. This feature allows the user to define cyclic or random upsets to view the effect of these events over time.

Test control, process

A completed model can be run in either real time for viewing in 2D or 3D or in a compressed time mode for a set period to gather operational statistics. Together these modes give the user a solid basis for evaluating system function.

An important capability of this package is the ability to interface with soft logic, where the model “control” is in the software programmable logic controller, and process dynamics are defined within AutoMod. This gives the added benefit of testing the proposed system concept and the control scheme prior to system commissioning.

This review is based on revision 9.1 of AutoMod from AutoSimulations operating under Microsoft Windows 98.

For related coverage, see ” Model, Simulate, Execute Simulation in Discrete Control ,” CE, April 2001.

For more information on AutoMod, Circle 312, or go online at www.controleng.com/freeinfo .

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