In this blog post, we’ll examine how technological uncertainty affects product quality, as well as the efforts mechanical engineers are making to overcome it and the importance of precision measurement technology.
Lego, which began in a small carpentry workshop in Denmark, is now a world-renowned toy loved by people all over the globe. Lego is a toy that allows children to build large, complex structures by stacking individual blocks. But did you know that important principles of mechanical engineering are at work behind the scenes in the Lego manufacturing process? Let’s take a look at the principles of mechanical engineering applied to the design and production of Lego blocks.
The blocks that serve as the basic building material for LEGO come in various sizes and colors. However, the most important feature they all share is “interlocking compatibility” with other blocks. Each block has a raised and recessed structure that allows it to easily connect to and separate from other blocks. If the size of these raised and recessed parts were inconsistent, preventing the blocks from fitting together properly, they would be nothing more than simple pieces of plastic.
People generally think that machines are much more accurate and precise than humans, but in reality, even the most precise machines inevitably have a certain tolerance for error. Just as putting dough into the same fish-shaped pancake machine produces pancakes with slightly different shapes each time, products will vary slightly even when using the same blueprints and production equipment. This phenomenon, where differences arise between scientific theories or designs and actual results, is called “uncertainty.” This uncertainty that arises during the product manufacturing process is called “technical uncertainty.”
Due to technical uncertainty, actual products are manufactured with dimensions that differ slightly from the design specifications, and these errors generally tend to follow a normal distribution. In other words, while most products are manufactured very close to the target dimensions, there is a low probability that some products will deviate significantly from the target. Errors are distributed around the target value (μ) with a standard deviation (σ); products closer to the target value are produced more frequently, while those farther from the target value are produced less frequently.
While errors caused by uncertainty are unavoidable, large errors can lead to various problems. In fact, when assembling LEGO sets, some blocks fit very tightly, while others fit somewhat loosely. This is because each block has slightly different dimensional deviations. If these deviations were to increase to the point where the blocks no longer fit together, the product would lose its value. To prevent such problems, mechanical engineers produce a certain number of prototypes before full-scale production to measure actual tolerances. For example, assuming that a block is considered defective if the size of its hole deviates by more than 5% from the design value, they manage the production process by investigating what percentage of the total production falls within tolerances of 1%, 2%, 3%, 4%, and 5%.
The most fundamental technology in this process of investigating such deviations is measurement technology. In everyday life, using tools that are not particularly precise does not pose a major problem. For example, when baking a pie, it doesn’t matter much whether the diameter is 16 cm or 16.1 cm. However, consider the small screws used inside a calculator or a watch: whether the screw’s diameter is 1 mm or 2 mm makes a very significant difference. As such, the production of precision machinery must, above all, be supported by precise measurement technology.
Such measurement equipment is collectively referred to as “measuring instruments.” The principle by which measuring instruments accurately measure length is based on “Abbe’s principle.” Abbe’s principle states that, to minimize errors when measuring length, the object being measured and the reference scale should be aligned as closely as possible along the same straight line. If we compare the case where the object being measured and the reference scale are placed side by side with the case where they are slightly tilted relative to each other, a difference in the measurement results occurs.
When applied to actual measuring instruments, an additional measurement error occurs when the object and the reference scale are tilted at a certain angle (θ) relative to each other, compared to when they are aligned side by side; the larger the angle of tilt, the greater the error. This principle is similar to the phenomenon where, when taking a photograph from an oblique angle rather than head-on, the subject appears with proportions different from reality. Although Abe’s principle appears very simple, it is widely used today as the fundamental principle of length measuring instruments because it reduces fundamental errors that occur during the measurement process.
According to Abe’s principle, measuring instruments suitable for length measurement are those designed so that the object being measured and the reference scale are as close to a straight line as possible. In actual manufacturing environments, various measuring instruments are used depending on the required precision. Tape measures or rulers are used for general measurements in millimeters (mm), while vernier calipers are used for precise measurements at the level of approximately 0.05 mm. When even higher precision is required, micrometers or dial gauges are used, and magnetic scales installed on machine tools and other equipment provide high precision capable of measuring down to the micrometer (μm) level.
From seemingly trivial items like LEGO blocks to the lids of household airtight containers, the fit of bolts and nuts, and the connection between USB cables and ports—if we take a closer look at the various products around us, we can see just how much technology has been applied to ensure that parts fit together precisely. Hidden within each of these tiny gaps is the relentless research and effort that mechanical engineers have devoted to minimizing potential errors.
When people think of mechanical engineering, they often imagine only grand technologies like transforming robots, cutting-edge satellites, or futuristic cars. However, mechanical engineering is deeply embedded in the design processes of everyday items we use—from ballpoint pen caps and umbrella frames to the conveyor belts at conveyor-belt sushi restaurants and even the very floor we’re standing on right now. Please take a moment to reflect on the role of mechanical engineers, who are constantly striving for precision and safety in the very places closest to our daily lives.
