New Generations of Computerized Handbooks Substantially Reduce Amount of Time Required for Common Engineering Tasks

Probably no task is as common in engineering as reaching for a reference manual or handbook, searching through it to find a section that applies to the task at hand, selecting a series of formulas, generating equations and then solving them with a calculator. The amount of time spent on this activity varies according to the specific duties of the individual but can easily amount to 25% of an engineer's day. Recently, the time required to perform this everyday function has been dramatically reduced through use of a new generation of general computerized handbooks covering fundamental engineering calculations, such as stress and deflection of basic engineering structures. In most cases, the program will do the equation substitutions, integration, and boundary condition analysis in exactly the way an engineer would solve the problem by hand. In some of the more complicated analyses, the computerized handbook uses finite elements to obtain a solution; however, the input and output format remains similar to the other modules and the user is not required to know finite element techniques. Moreover, once a problem is accurately set up and modeled, it can be quickly changed and rerun to allow the user to look at various options or modifications.

A good example of the benefits which can be achieved by programs of this type is provided by the experience of the Trionix Research Laboratory, Inc., Twinsburg, Ohio. When this company conceived of a revolutionary new nuclear diagnostic imaging camera design, they immediately found a buyer for the first machine -- if they could ship in six months. Nuclear diagnostic imaging cameras normally require two side-by-side scans to image each side of the body along its length. Trionix's concept was to image the entire length and width of a patient on both sides in a single pass and also provide cross-sectional images. This would reduce the time required for a full body scan from one hour to twenty minutes which would naturally greatly reduce the cost of the procedure. According to Carlos Pinkstaff, Principal Mechanical Engineer, the six-month goal was met largely due to the use of The Desktop Engineer, a computerized engineering handbook. With the computerized handbook, Pinkstaff was able to compress convoluted stress and strain calculations which would have taken days or weeks by hand into minutes or a few hours.

A key to the new design was increasing the diameter of the opening to 36 inches which allows the patient to lie with his arms at his sides and, even more important, allow the camera detectors to cover the entire body width. The problem with simply scaling up the old design was that the ball bearing cost would increase by a factor of six. So Pinkstaff developed a new concept in which a 45 inch inside diameter ring would carry the detectors and in turn be supported by vee-groove type cam rollers mounted in a circular array and supported by a gantry. The ring represented an exceptional design challenge since it had to carry the two 650 pound detector heads and two 500 pound collimators for a total of 2300 lbs. The ring also had to have as little inertia as possible in order to allow It to be rotated quickly about the body. In Pinkstaff's concept, the ring is a composite ring whose primary member is a steel gear which functions both as part of the driving mechanism and also as structural member. Bolted to the gear is an aluminum ring which enhances the stiffness of the assembly.

Pinkstaff said that he has found curved beam calculations like this one to be a horrendous job when performed by manual methods. Performing the necessary stress and deflection calculations on the ring would have easily taken two weeks by hand, he said. Pinkstaff said that the last time he faced a similar problem he spent one day doing one iteration by hand. Then he spent a week writing a computer program that would handle further iterations. However, when this project arose, he had just purchased The Desktop Engineer. After a few hours spent studying the manual and example problems, Pinkstaff turned his attention to the ring and completed his first iteration in only 10 minutes.

The program works like this, Pinkstaff said: "You define the geometry of the structure in two-dimensional space, enter anchor points and types of joints, apply loads by giving a force vector and a moment

and observe the deflection." Further iterations took only a few minutes as he merely changed the desired parameter and re-ran the calculation. Pinkstaff completed the entire analysis process which involved about 40 iterations in about a day. Pinkstaff said that the wide range of modules in The Desktop Engineer offers unusual flexibility in attacking structural problems. For example, when he found that he couldn't achieve the exact loading effect he was seeking with the "ring module," he switched over to the "arch module" and modeled the ring as two arches linked together with built-in ends. Test results showed no movement at the ends which validated this unusual approach.

As another example of the benefits which can be achieved through this technology, FMI, a Novato, California packaging and filling machinery manufacturer, has reduced typical time required to perform deflection and stress calculations by 75%. 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. Design of these machines involves the synthesis of a wide variety of technologies including pneumatics, hydraulics, robotics, thermodynamics, motion control, and many others, according to Roger Sinsheimer, Technical Director for the firm.

Sinsheimer said that soon after he purchased The Desktop Engineer, a computerized engineering handbook he solved a problem that by itself more than 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 similar 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.

The Design Engineering Technology Group of Mobay Corporation's Plastics and Rubber Division, in Pittsburgh, Pennsylvania, is responsible for offering assistance to customers in their design of components using the division's polymer materials. Brian Dowler, Design Engineer for Mobay, was recently asked to analyze a set of two medical cannisters molded of Mobay's Makrolon polycarbonate resin. The analysis was required because the Bannisters, which basically consisted of 1500 cc and 2500 cc cylinders, were failing a vacuum implosion test. The test consisted of generating an initial vacuum of 17 inches of mercury inside the cylinders which is equivalent to 8.35 psi, then pressurizing the outside until the walls of the cylinder failed. The larger cylinder was to withstand a total pressure of 22.35 psi and the smaller cylinder was to withstand 21.35 psi. Both cylinders, which were originally molded with a wall thickness of .080 inch, were failing very close to the specified pressure value. Dowler was asked to determine the minimum wail thickness that would provide adequate wall strength with a 2056 margin of safety.

Dowler pointed out that the conventional equations for solving cylinder buckling problems are quite lengthy, particularly when considering that they have tube solved for different waves in each load case. He estimated that writing, solving and checking the equations by hand would have taken about a day. Instead, using the "cylinder buckling" module of The Desktop Engineer, he solved the complete problem in about 15 minutes. The procedure simply involved entering the height, diameter and thickness of the cylinders and the strength of the polymer. Based

on these values, the program predicted a buckling pressure of 22.9 psi in the smaller cylinder which was remarkably close to the test results. Dowler then entered a new thickness value of .091 inch and ran the analysis again. The new pressure value was 30.5 psi which, although it exceeded the specification, did not provide an adequate margin of safety. Further increasing the thickness to .100 inch yielded a pressure value of 38 psi which did provide the necessary safety margin and ended up being the final recommended design value. An analogous procedure was used for the larger cylinder.

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