Look a little closer
See the mechanism
A rotating crank drives a reversing shaft
Read the diagram steps
One crank phase. The rotating eccentric pulls the connecting rod. The rod turns a rocker about its fixed pivot; a shaft carries that limited rotation toward the head.
Opposite crank phase. The eccentric reaches the other part of its orbit, pushing the rod back. The rocker, shaft and brush carrier reverse instead of making full continuous turns.
Original functional schematic; dimensions and motion are exaggerated, not measured. Four-bar and bevel-gear example from a historical patent. The two views are separated and use different scales; no clinical effect is depicted.
Diagram basis: US5311633A: Figures 1–4, eccentric/link/rocker and bevel gears.
Sources: Braun GmbH
A rotating disk makes a rocking movement
Braun's patent describes a four-bar linkage inside the handle. The disk turns continuously, but its connection to the rod travels around an off-center path. The rod pushes and pulls the rocker, whose shaft turns through an arc and then reverses.
Sources: Braun GmbH
The motion changes axis at the head
The shaft runs along the neck. At its end, a pair of bevel gears connects it to the brush carrier, whose axis lies roughly at a right angle. As the shaft reverses, the carrier reverses too; the bristles do not need to make complete revolutions.
Sources: Braun GmbH
The thing to remember
The linkage makes the reversal; the bevel gears redirect it toward the brush face.
What this example leaves out
This is a documented crank-and-rocker design, not every electric toothbrush. Other drives produce different movements.
Sources & further reading
Source access dates are listed below. Manufacturer descriptions and patents support the specific constructions described, not every product.
- Electric power driven toothbrush (US5311633A) ↗
Braun GmbH · Retrieved 2026-10-18 · Motor rotation converted by eccentric disk, connecting rod and rocker into shaft oscillation; bevel gears turn axis to brush head.
Read preferred embodiment, parts 2, 8, 10, 12, 14, 15 and 25–32; figures 1–4 described in patent. Historical design example only, not identification of a current product; no clinical claims adopted.
