Machines that use no power
Karakuri kaizen, or mechanism improvement (からくり改善), solves a shop-floor problem without electricity, air or hydraulics. It uses gravity, human motion, springs and magnets.
JIPM, Japan’s plant-maintenance institute, sets the rules. The device must be cheap and safe, and the operators must build it themselves. The toolbox is eight simple mechanisms: lever, cam, pulley, linkage, gear, screw, wheel and inclined plane.
It started with a tea-serving doll
In the Edo period, Japanese craftsmen built tea-serving dolls (茶運び人形, chahakobi ningyō). A whalebone spring and wooden cams drove them.
The craft passed to Tanaka Hisashige, known as Karakuri Giemon. His company later became Toshiba.
Toyota’s founding machine was a karakuri
Sakichi Toyoda’s 1924 Type G loom ran on about 25 purely mechanical mechanisms. One stopped the loom when a thread broke, so a weaver no longer had to watch each machine.
That stop is the mechanical root of jidōka, automation with a human touch (自働化).
How a gravity return chute works
The device below is a simplified gravity return chute (重力返却シューター, jūryoku henkyaku shūtā). A full tray of parts slides down to the operator. Its weight tips a counterweighted lever, and the empty tray rolls back down the return rail.
Full totes queue on the upper lane. The front one sits on the cradle, held down by its own weight.
It is modeled on a real device at Toyota’s Motomachi plant that delivers instrument-panel trim. It replaced an automated guided vehicle. It is made of a pipe rack, rollers, fishing line and a weight, and its team won a company award of about ¥20,000.
Five devices from real plants
Each of these does a job that would otherwise need a sensor, a motor or a robot.
- Two-screw feeder, Toyota
- The screwdriver’s weight dips a magnet that picks up exactly two screws. It checks the count with no sensor.
- Return cart, Toyota
- Loading the cart lifts a counterweight. Unloading releases it and sends the cart home, saving 8 walking steps a cycle.
- Pendulum feeder, Toyota Boshoku
- It cost about ¥50,000 to build. The powered feeder it replaced would have cost ¥1,000,000.
- Lever lift cart, Umemura
- A long lever cuts the force needed to lift heavy dies by about 75%.
- Press-crank air generator, Toyota
- The press’s own crank motion makes compressed air, saving 2.85 tonnes of CO2 a year.
Japan holds a national contest for them
JIPM has run the Karakuri Kaizen Ingenuity Exhibition (からくり改善くふう展, Karakuri Kaizen Kufū-ten) since 1994. Toyota group companies won the grand prize three years running.
Toyota Motor Kyushu goes further. It certifies staff as “Karakuri-man” and ties the title to promotion.
- 2022Toyota Industries, for the little hill-climber (坂道のぼる君, Sakamichi Noboru-kun). Sliding an empty box onto the rack lifts the next box to hand height.
- 2023Toyota Motor Kyushu.
- 2024Toyota Auto Body, for the love elevator (恋のエレベーター, Koi no Erebētā).
Why Toyota wants more of them now
Toyota aims for plants with zero CO2 emissions by 2035. Toyota Times calls karakuri “the ultimate carbon-neutral device,” because each powered conveyor it replaces stops using energy for good.
A device with no power cable, air line or control cabinet can also move in minutes when a line is rebuilt. The operators who built it maintain it.
The opposite of a dark factory
In a dark factory, automation is bought, and few people on the floor understand it. In karakuri, the people who use a device build it, so each one is a lesson in how the work is done.
Kawai Mitsuru rose from apprentice to Toyota executive. He says, “To be the master of the machine, you have to have the skills to teach the machine.”
None of this needs a car plant. A gravity chute works the same way in a hospital supply room or a warehouse pack station.