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Construction

Robot and apprentice: Preserving the art of Japanese joinery

Aging artisans push contractor Shimizu to digitize tradition for a new age

Joinery methods that use no nails or glue are a feature of traditional Japanese architecture, which use raw wood. (Photo courtesy of Shimizu)

UTSUNOMIYA, Japan -- Traditional Japanese joinery is a precise craft. Instead of using nails or glue, joints are cut into complex designs that fit together like a perfect Tetris puzzle.

The centuries-old technique -- called shiguchi -- delivers both beauty and function. The joints between a building's pillars and beams bear a lot of weight and can damage easily. Interlocking them to increase the area of contact helps alleviate the strain and strengthens the overall structure -- a particularly important consideration in an earthquake-prone country like Japan.

Historically, these special joints have been chiseled and planed by the hands of experienced craftspeople. But with many carpenters aging out of the industry, Japanese contractor Shimizu is developing a robot to keep the tradition alive for years to come.

There are pros and cons to Shimizu's high-tech strategy. On one hand, the wood needs to be repositioned several times for the robot to make cuts in different directions. On the other, the robot is capable of extreme precision and accuracy, especially when it comes to curved surfaces.

Rather than reproducing traditional joint patterns, Shimizu aims to create new methods that make use of robots' advantages, passing on traditional skills in a new form.

Shimizu is developing a robot that can carry out the tradition of shiguchi joints. (Photo by Go Sakurai)

One of its innovations is joining beams together by cutting their edges into semicircles, instead of more angular edges that can be difficult for the robot.

Another is to shape the wood in a way that essentially allows one piece to screw into another. Traditional shiguchi joints are usually designed to be put together in a straight line or at a 90-degree angle. But the new rotational approach gives builders more flexibility in putting joints together and to better maneuver in tight spaces.

Shimizu's effort comes amid a pressing shortage of human artisans able to handle wood joinery.

The construction industry is grappling with an aging pool of craftspeople, and needs an influx of new talent to inherit these skills. But young people are reluctant to enter a field seen as difficult, dangerous and dirty. Companies are responding by using robots to improve working conditions, either by providing support or handling certain tasks.

A shiguchi joint cut by Shimizu's robot: the company is working on new patterns that are better suited for robots. (Photo courtesy of Shimizu)

The shiguchi robot has a slightly different purpose -- directly mechanizing the work of artisans. While the shortage of craftspeople was the impetus for their development, the project has gone beyond passing on traditional skills, leading to the development of completely new forms of joinery.

Shimizu also aims to promote broader use of wood in construction.

The construction industry has a major role to play in Japan's decarbonization efforts. According to Shimizu, wood construction generates less than half the greenhouse gases of reinforced concrete per cubic meter, and a third less than steel-frame buildings. Wood also has the advantage of storing the carbon dioxide absorbed by trees as they grow.

The lighter weight of wood compared with concrete reduces the amount of work needed for a building's foundation as well. But because lumber itself is pricier, the overall cost remains relatively high. Changing this will require new technology that expands the contexts in which wood can be used, bringing down its price and driving a virtuous cycle.

Shimizu aims to start using new shiguchi techniques next year after testing their strength with full-size models.

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