High-Speed Projectors Power This Virtual Air Hockey With Shape-Changing Paddles

High-Speed Projectors Power This Virtual Air Hockey With Shape-Changing Paddles

If you’ve spent any time at a modern arcade you’ve probably seen air hockey tables upgraded with glowing pucks and paddles that make the game more visually appealing. Researchers from Tohoku University in Japan have taken those upgrades one step further in a version of air hockey that replaces the pucks and paddles with shape-changing virtual projections that increase the challenge.

It’s an idea we’ve seen with billiards tables as well, where a projection system mounted above the table creates animations and effects in response to the movement of the balls, and in some cases, provides visual aiming cues for players setting up their next shot. But to date, these upgrades have all been reactionary and simply enhance a game of pool by tracking the movements of traditional cue sticks and billiard balls. What the researchers from Tohoku University’s Intelligent Control Systems Laboratory have created is a modern twist where the projection system completely replaces the physical parts of air hockey.

A semi-transparent and rigid rear projection screen replaces the traditional air hockey table surface that’s normally perforated with holes to let air through. Being semi-transparent not only allows projections on the underside of the table to show through (a better approach than projections from above that can be obscured by the player) but it also allows a camera underneath to track the movements of the player’s paddle, which features a bright infrared LED so that its orientation can be easily seen and tracked, even in low-light conditions.

The use of a projector and a video camera isn’t the notable innovation here that makes MetamorHockey appear so highly interactive and accurate. What makes these upgrades work so well is that the projector and video camera both work at an astonishing 420 frames per second. So during every second of gameplay, the video camera is detecting the position and orientation of the player’s paddle 420 times, feeding that information to a computer that calculates the movements and trajectories of the virtual puck, and then it passes that data to a projector that refreshes the position of the virtual puck and paddle the same number of times each second.

Even a projector running at 60 frames per second would make the player’s paddle appear to lag behind the high-speed movements of the handle they’re holding as they play, which would make the virtual air hockey experience feel less authentic and less enjoyable. The extremely high frame rate of the custom low-latency DMD (digital micromirror device) projector used here is fast enough to fool a player’s eyes into believing the virtual paddle is locked to their movements, which sells the effect.

Does air hockey need an upgrade? Probably not, but MetamorHockey’s virtual puck will never fly off the table like the real ones have a tendency to do, which is certainly one advantage. And being able to change the size and shape of both the puck and paddle on the fly does introduce some interesting ways to change the way air hockey is played. Irregular shapes make it harder to reliably predict which direction the puck is going to travel, increasing the challenge, while increasing the size of the paddle could make it easier for less experienced players to actually enjoy playing against someone who’s more skilled at the game.

There’s no word on when MetamorHockey might show up at your local arcade, but more details will be revealed when its creators present their research at the upcoming Siggraph 2021 conference in August.