Roger Sinsheimer
Technical Director, FMI

FMI, a Novato, California packaging and filling machinery manufacturer, has reduced typical time required to perform deflection and stress calculations by 75%. This was accomplished with a new "computerized engineering handbooks called The Desktop Engineer (Desktop Engineering/Computer Aided Analysis, Solutions for Engineers marketed by Desktop Engineering, Inc., Woodcliff Lake, New Jersey). Roger Sinsheimer, Technical Director for FMI, says the software package provides the perfect solution for the vast majority of engineering calculations faced by the firm which aren't complex enough to warrant time-consuming finite element modeling yet are extreme! y tedious to solve by hand.

FMI produces machinery that provides automated packaging of extremely critical food and pharmaceutical products such as synthetic blood and other biologically active fluids which must be handled in totally sterile conditions and cannot be heated or irradiated to achieve sterility Previously, such products had to be packaged by hand within a laminar flow hood in glass containers that cost about $25 each. The ability to automate this process and use plastic bags as containers offers the opportunity for substantial cost savings as well as improved quality control. Container cost can be reduced to about $5 and there are also substantial labor savings.

Design of these machines involved the synthesis of a wide variety of technologies including pneumatics, hydraulics, robotics, thermodynamics, motion control, and many others, according to Sinsheimer. To illustrate the point, he cites the company's library of supplier catalogs which occupies a medium sized room. He said that the engineering calculations involved in designing a machine of this complexity would have quickly overwhelmed his small engineering staff. Yet, he felt that nearly ail of the calculations he faced weren't complex enough to merit lengthy training and modeling time and high software cost involved with finite element analysis.

"Then I heard about a low-cost product called The Desktop Engineer that provides canned solutions to a wide range of engineering problems while avoiding the necessity of creating a finite element model," Sinsheimer said. "I purchased the product and found it offered a wide enough range of modules -- such as beams, columns, plates, shells, rings, cables, arches, etc. -- to handle virtually all of our needs. Furthermore, the product makes it possible for us to solve fairly complex assemblies by combining various canned situations. In fact, throughout the design cycle of our most recent machine, I never found a single situation where The Desktop Engineer couldn't give me the answer. The software provides deflection results much, much faster than traditional finite element analysis and also allows us to try out a wide range of what-if possibilities in minimal ti me. "

Sinsheimer said that he solved his first problem with The Desktop Engineer on the day he received the software and that this one application alone paid for the $945 cost of the software. "I needed to design a simple, yet rigid frame to support an air cylinder capable of exerting up to 150 pounds of force. If the cylinder moved more than a few thousandths of an inch when applying that force, the final product would be ruined. Normally, this would not be a difficult design problem, except for the additional requirements that the cylinder be mounted several feet up and several feet out from the nearest part of the machine capable of supporting these loads."

Sinsheimer simulated the frame using the general frames module of the program. "The program works like this," Sinsheimer said. "You define the geometry of the frame in 2D space, enter anchor points and types of joints, apply loads by giving a force vector and a moment and observe the deflection. The first iteration showed acceptably low deflection, yet I wanted to optimize the structure, not settle for good-enough. So, I plugged in half a dozen different cross-sectional values until I was sure I had the smallest value that was stiff enough. This entire process took less than a day, but that included learning the program as well." Sinsheimer said he now solves similiar problems in about half an hour for the first iteration and five minutes per additional iteration.

In another typical application, Sinsheimer used the circular plate module of the program to determine the optimum thickness for a Plexiglass window used in a vacuum chamber that FMI uses to prepare silicone cement to fasten endless silicone belts used in the making machine. Sinsheimer obtained materials properties on the Plexiglass from the manufacturer and entered the data into The Desktop Engineer material property database. He then applied a load of 14.7 psi across the 9" diameter plate. Just a few iterations determined that 3/4" was the optimum thickness value.

As a final example, Sinsheimer cited the case of "dancer arms used to advance the plastic web material which is converted into a bag by FMI's machine. One of Sinsheimer's co-workers, Mike Gaskell, needed to minimize the weight of the carbon fiber dancer arms in order to avoid tension spikes under low tension conditions during high speed operation. This problem was solved with the thin wall cylindrical shell module of The Desktop Engineer applied in the usual manner. Gaskell did a first pass guess on the tube structure, then re-ran the analysis while varying the tubing diameter until the optimum of .300 inch diameter was determined. He notes that this problem would have taken days to work out by hand, while he solved it in three hours with the computerized hen d book.

The Desktop Engineer is basically a computerized handbook of solutions to over 5000 structural/mechanical engineering equations found in over 100 reference books. It includes 37 modules grouped into the following categories: geometric and material properties; beams and columns; rings, cables, arches and frames; plates, shells, and pressure vessels; natural frequencies; miscellaneous; user defined modules; and utilities.

Modules are self-prompting to help the user find or calculate things like material properties, inertial, etc. Once the problem is thus defined, the program will do the necessary calculations and solutions to provide the necessary output. In most cases it will do the equation substitutions, integration, boundary condition analysis, exactly lice one would do if the problem was done by hand. In some of the more complicated analyses, the program uses finite elements to get a solution, even though the input and output format remains similar to the other modules and the user is not required to know finite element techniques. Once a problem is accurately set up and modeled, it can be quickly changed and rerun to allow the designer to look at various design options or modifications.

Several utility modules are included to assist the designer with complex problems. A superposition module allows the designer to look at the effects of several concurrent loads on the same structure. A module is included to produce Mohr's circle analysis for multi-axial states of stress and strain. Modules are also included to assist the user with calculating section properties, The program also has a convenient material database and several modules that look at complex geometries and dynamic conditions. Although the program is self-explanatory, the user manual is well-written and includes a theoretical section which provides the equations and references for the entire system.

The Desktop Engineer operates on most computers using Windows and supports color high resolution graphics for the IBM PC, AT, PS/2 and compatibles.