Function of spiral spring

Spiral springs are generally used as the power source for miniature machinery without electric energy. Examples include the power for timekeeping and striking systems in mechanical clocks, the driving force that spins records in mechanical gramophones, mechanical music boxes, self-playing pianos, and wind-up toys. Machinery powered by such spiral springs share a common feature: their transmission chains are speed-increasing mechanisms, rather than the speed reducers commonly used in other machinery. Additionally, a spiral spring delivers a large torque when fully wound, while its output torque drops significantly as it nears full unwinding. To mitigate this uneven torque output of the spring, all such devices are equipped with a speed governor to stabilize the rotational speed of the mechanism. In mechanical wristwatches, to reduce this torque disparity, the mainspring is specially shaped into an S-shape in its free state instead of a flat equidistant spiral, which balances the output torque of the spiral spring to a certain extent.

When designing spiral springs, multiple factors must be referenced to select specifications from relevant design manuals, including the minimum driving torque, the maximum allowable torque, the torque and rotational speed required by the final driven actuator, and the total required operating duration. The dimensions of the spring barrel, as well as the module and tooth count of gears, are also determined in this process. After prototype testing, all component parameters are revised and finalized accordingly.