At ten each night the lights go off in Hall 3 of Hanegawa Seiki's plant outside Kani, in Gifu Prefecture. The machines keep going. For the next eight hours, 46 robot cells machine, wash and inspect aluminium housings for car steering units, and the only light on the floor comes from status lamps and the blue flicker of the welding station at the far end.
The film above follows one night in the hall, from the last walk-through to the arrival of the morning shift. Below: what it takes to run a factory with nobody on the floor, and what it saves.
Lights off at ten
Hanegawa Seiki makes precision parts for Japanese car and machinery makers and employs about 340 people. It built Hall 3 five years ago for what the industry calls lights-out production: work that runs unattended for a whole shift. Here the phrase is literal. Robots do not need ceiling lights, and the cameras that inspect the parts carry their own.
The plant manager, Sayaka Morimoto, does the last walk-through herself on most nights. She checks the bar-stock feeders, the coolant levels and the reject bins, then locks the hall and switches off the ceiling panels from a key box by the door. "In the first few months I came back at midnight to look through the window," she said. "Now I go home."
What the robots need
An unattended cell is designed around whatever might stop it. Each one holds enough raw stock for nine hours. Cutting tools are monitored for wear and swapped automatically from a magazine of spares. Aluminium chips, the enemy of every machining line, ride away on conveyors so they cannot pile up around the spindle.
The weak points are the ones nobody planned for. A delivery of bar stock slightly out of tolerance jammed four feeders in one night last winter. A spider built a web across a light curtain and triggered a safety stop at three in the morning. Both problems were fixed within weeks, and each cost a night's output from the cells involved.
The energy bill
Morimoto's team measured Hall 3's electricity before and after the switch to unlit nights. Lighting had been about 7 per cent of the hall's load. Air conditioning for people was another 11 per cent; at night the hall now runs in a wider temperature band, kept only as cool as the machines need to hold their tolerances. By the company's figures, the night shift uses about 16 per cent less power per part than the day shift.
The saving is smaller than it sounds. Spindles, pumps and compressors dominate the bill, and they run regardless. The larger change was in the cost of the night itself: a night shift of 18 operators became a crew of three.
Three people on call
The night crew sits in a control room across the yard, facing a wall of dashboards and one camera feed per cell. Their job is to respond. When a cell stops, its tile on the screen turns amber, and one of them walks over with a torch and a tablet.
Daisuke Oka, a maintenance technician who used to run a lathe on the day shift, has worked nights in the control room for three years. He says the hardest part is the quiet between alarms. "On a good night nothing happens for six hours," he said. "You have to stay ready for the one thing that does."
The fifteen operators who used to work nights moved to day shifts, programming and quality control. None were laid off, Morimoto said, though the plant has not replaced people who retired.
What the output says
Hall 3 turns out about 21,000 housings a night, against 23,500 on a staffed day shift, which also handles changeovers and first-article checks. Scrap is lower at night, 0.4 per cent against 0.7, because nobody opens a guard door and the temperature holds steadier. Morimoto expects the output gap to narrow as the hall learns. Hanegawa plans to run a second hall the same way next year.
For more from the places where goods are made before they ship, see the heat pump factory town and the pallet economy.
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