Signal transmission device for articulated mechanism

A robotic arm comprising:

• at least pair of structural members rotatably coupled to one another for rotation about an axis of rotation, with a first one of the structural members having a hollow shaft defining a central passage generally extending along the axis of rotation
• a motorized joint unit surrounding the hollow shaft and configured to drive a rotation between the structural members about the axis of rotation;
• a communications link at least partially within the robotic arm for signal transmission within the robotic arm, the communications link including
• a signal transmission device having a coiled portion, with ends of the coiled portion adapted to be connected to parts of the communications link, whereby the coiled portion is a segment of the communications link, and an elongated portion extending from one of the ends of the coiled portion into the hollow shaft,
• wherein the coiled portion has one of its ends connected to a second one of the structural members to rotate with the second one of the structural members, the elongated portion connected to a component associated with the first one of the structural members through the hollow shaft to rotate with the first one of the structural members, at least a portion of the coiled portion expanding or contracting radially during relative rotation between the pair of structural members.