Samsung Files Patent for a Robot Finger That Bends and Straightens With One Motor
Samsung's filing describes a three-joint robot finger that bends and straightens using one motor and one loop of cable. A second set of motor-free cables and a spring lets it give way under pressure and spring back.
What Samsung's one-motor robot finger does
Imagine a robot working behind a café counter, closing its fingers around a paper cup. Each finger has to curl around the cup and open back up, and every motor you add makes the hand bigger and more complicated.
Samsung's patent application describes a robot finger that does both jobs with one motor. A single cable loops around a pulley at each joint. One stretch of it runs along the back of the finger, the other along the palm side. Turn the motor one way and the back stretch shortens, so the finger straightens. Turn it the other way and the palm-side stretch shortens, so the finger curls around the cup.
A second set of cables and a spring work without any motor. When something pushes on the finger, the joints give together and then spring back once the push stops.
an extension cable that is wound in a first direction along a back side of the finger at each of the plurality of active pulleys; and a bending cable that is wound in the first direction along a palm side of the finger at each of the plurality of active pulleys …
Translation: One cable runs along the back to straighten the digit while another runs along the palm to curl it.
How Samsung's cable loop curls the finger
The finger is built from frames (bone-like segments) joined end to end by three shafts (hinges) at the tip, middle and base joints. Each hinge carries a pulley (a grooved wheel the cable rides in), and one actuator (a motor) drives all three through a single cable.
The cable is split in function only. One stretch, the extension cable, runs along the back of the finger. The other, the bending cable, runs along the palm side. Both wrap each pulley the same way, and since the total length is fixed, whatever one gives up the other gains. Turn the motor one way and the finger straightens; turn it the other and it curls. A tensioner in the fingertip takes up slack as the cable stretches with use.
A second set of cables needs no motor. One, named for the oblique retinacular ligament in a human finger, links the tip and middle joints so they move together. Another, named for the lumbrical muscle, links the middle and base joints and keeps the middle joint from over-curling in a pinch. A torsion spring (a coiled spring that resists twisting) returns everything when the pressure ends.
The claims also cover a full hand, with motors packed in the palm and a thumb module of its own, and a robot with a body, an arm and legs or wheels.
When the actuator rotates in a first direction, a total length of the extension cable decreases, and when the actuator rotates in a second direction, a total length of the bending cable decreases.
Translation: A single motor turns back and forth to pull opposing cables that control the straightening and bending.
What fewer motors could mean for robot hands
The filing's own background says robots are being developed to stand in for people in shops, cafes and restaurants. A finger that curls all its joints from one motor means fewer motors to pack into a palm. The spring-loaded cables also let a finger give a little when it bumps into something, then return to shape.
The filing names no product and gives no figures on grip strength or cable life, so treat it as a design sketch for now. The extra tensioner does hint that cable stretch is a maintenance concern the designers took seriously.
Samsung's 56th filing we've tracked since May in our home robot watchlist adds to work like turning maps into 3D plans and pre-heating mop water.
Robot hands are hard to build because a human hand packs a lot of joints into a small space, and every joint that needs its own motor adds bulk, wiring and parts that can break. Samsung's filing goes after that directly: one motor per finger, one cable loop, and all three joints follow.
The fix fits the size of the problem. It copies just two tricks from the human finger, the tip joint following the middle joint and the middle joint resisting over-curl, and handles them with plain cables and a spring.
The weak spot is that cables stretch, and the filing admits as much by adding a tensioner that has to be turned by hand or by a small motor. With no numbers on grip strength or wear, you can't yet judge how well it works. It is a sound idea aimed at a real problem, still unproven.
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The drawings
21 drawing sheets from US 2026/0326284 A1 · click any drawing to enlarge
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