Machine Design

Software automates back-of-the-envelope calculations

An engineer used GrafiCalc simulation software to define the concept for a machine intended to punch-out dog food biscuits. The software lets users “pre-model” designs before CAD by drawing skeleton geometries that represent the design’s functional intent — not its form. The process has been likened to sketching on the back of an envelope. GrafiCalc simulates and solves kinematics. As well, it handles static and tolerance stack-up analyses and includes technology that helps optimize designs against shape, position, and fit criteria.

The initial challenge in the design of the dog-biscuit machine was to establish the equations for servomotors so the bottom end of a lapper arm moved at a constant velocity as a punch lowered. The user first sketched the skeleton geometry and constrained it to reflect the functional intents. The engineer then back-solved the geometry of the mechanism using inverse kinematics to establish constant velocity for the end of the lapper arm. The user imported the transient values of the length of the actuator into Excel to develop the equations of the servomotors. The software thus helped the user conceptualize, analyze, and validate critical engineering parameters in the earliest stages of design.

According to the engineer, running the analysis took about an hour to get the optimal solution with GrafiCalc. In contrast, the engineer estimated a design time of about one month using the “build-text-fix” method with a mid-range CAD package, a motion-simulation add-on, and data-analysis software.

Sources: Geomate Co.,

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