Most massage chairs rely on a combination of motors, gears, rollers and vibrating mechanisms. This kind of chair dates back more than half a century. Over the last few decades they've become much more sophisticated.
The simplest massage chairs use a series of vibrating surfaces to provide a massage. To create the vibrations, manufacturers use small devices that contain a weighted wheel or gear. The weight isn't centered on the wheel, which makes the wheel unbalanced. When the device's electric motor rotates the wheel rapidly, the rotation causes a vibration. Cell phones with a vibrating feature contain a small version of this kind of device. A massage chair needs several of these devices to generate vibrations across its surface without unbalancing the entire chair.
While no two massage chair manufacturers use the exact same design, there are some general design techniques that apply to most models. If you were to strip away the upholstery of the chair, you'd see a frame that supports a system of motors, gears and rollers.
When you're getting a massage from a massage chair, it's the rollers that act like a human's hands. The rollers move in patterns determined by the structure of the frame. Some massage chairs rollers have a limited range of motion -- they can only move up and down the back of the chair because they travel along a track attached to the frame. Electric motors provide the energy for the rollers.
Other massage chairs have more complexity. On these chairs, the manufacturer mounts the rollers onto a mechanical arm that can move laterally as well as vertically. This means the rollers can move left and right, or even in circles. Again, an electric motor powers the mechanical arm's movements. A microprocessor in the massage chair stores recorded patterns the manufacturer pre-programs into the chair.
Many massage chairs allow the user to adjust the intensity of the massage. There are two main ways to adjust the intensity. One is to change how far the rollers move away from the frame when in massage mode. The second is to mount the frame on a pivot in the backrest, allowing it to move closer to or further away from the user's back.
Since many massage chairs are recliners, manufacturers have to design electrical and mechanical systems that can operate in multiple positions. Some massage chairs have a motorized reclining system. The user can change the chair's position by pressing a button on the massage chair's control system. Other chairs require the user to pull a release handle before physically pushing back against the backrest of the chair.
Not all massage chairs rely on a purely mechanical approach. One design uses water, yet users stay completely dry. How does that work? Find out in the next section.