How Exoskeletons Use Screws and Cables to Move Joints

This patent describes a mechanical system for exoskeletons that uses a rotating screw to push a nut, which then pulls cables to make a joint bend or straighten.

What it covers

The patent describes an exoskeleton joint actuator that connects a first support (like a torso brace) to a second support (like an upper leg support) via a joint (such as a hip joint, claim 10). The actuator includes a "ball screw" and a "ball nut assembly" that moves along the screw (claim 1). This ball nut assembly is connected to "at least two tensile members," which are like strong cables. When the ball nut assembly moves in one direction along the screw, it pulls on these tensile members. This pulling action causes the second support to rotate in a specific direction relative to the first support around the joint. Moving the ball nut assembly in the opposite direction makes the joint rotate the other way, allowing for controlled bending and straightening of the exoskeleton's limb.

What it doesn't cover

• —Exoskeletons that use hydraulic or pneumatic cylinders for joint movement instead of a ball screw and tensile members.
• —Joint actuation systems that use rigid linkages or gears directly to move the supports, rather than flexible tensile members.
• —Actuators that rely on only a single tensile member to create bidirectional joint rotation.
• —Systems where the tensile members are not routed with portions extending in opposite directions from the ball nut assembly, or not on opposite sides of the ball screw (claim 1).
• —Exoskeletons where the joint does not include a joint pulley connected to the tensile members (claim 2).

The clever bit

The novelty lies in efficiently converting the linear motion of a ball nut along a screw into powerful, bidirectional rotational motion at a joint using a specific arrangement of multiple tensile members. This allows for a compact and robust design for controlling exoskeleton joints.

Why it matters

This type of actuation is important for exoskeletons because it allows for precise and powerful control of movement. Exoskeletons, like those made by Ekso Bionics, help people with mobility challenges or assist workers in physically demanding jobs. A reliable and strong joint mechanism is crucial for safety and effective assistance, enabling users to walk or lift with support.

Real-world examples

• 1.Ekso Bionics EksoNR exoskeleton
• 2.Industrial exoskeletons for lifting assistance
• 3.Rehabilitation exoskeletons for gait training