Power transmission method and device having load sensing thrust augmentation mechanism

A power transmission device for converting a rotational motion of an electric motor into a linear motion, the device comprising:

• a feed screw that is connected to an output shaft of the electric motor so as to rotate;
• a female screw having an effective diameter that is larger than an effective diameter of the feed screw;
• a moving case whose relative rotation is restrained with respect to rotation of the feed screw;
• a bearing for supporting loads in the radial direction and in the axis direction so that the female screw can rotate in the moving case and can slide in the axis direction;
• and
• a spring element for pressing a brake disk that is disposed in the moving case and is attached to an end surface of the female screw integrally onto one of inner surfaces of the moving case, wherein
• the feed screw penetrates bearings that are disposed at both end covers of the moving case and is arranged in an eccentric manner from the female screw housed in the moving case, and
• when the moving case receives a counterforce from a load so that a thrust generated on the female screw becomes larger than a pressing force of the spring element, the female screw moves in the axis direction with respect to the moving case so that the brake disk separates from one of the inner surfaces of the moving case, and that the restraint of relative rotation of the female screw with respect to the moving case is released, and that the feed screw and the female screw rotate in a differential manner.

A power transmission device for converting a rotational motion of an electric motor into a linear motion that is transmitted to a load, the device comprising:

• a feed screw that rotates by an output of the electric motor;
• a moving case through which the feed screw penetrates in the axis direction, the moving case being rotatable relatively to the feed screw so as to transmit a thrust along the axis direction of the feed screw to a load;
• a female screw disposed in the moving case, the female screw having an effective diameter that is larger than an effective diameter of the feed screw so as to generate the thrust by engaging with the feed screw in an eccentric manner;
• a bearing disposed in the moving case for supporting the female screw in a rotatable manner relatively to the moving case, the bearing itself being capable of moving in the axis direction with respect to the moving case;
• a brake shoe fixed to the moving case for restraining relative rotation of the female screw with respect to the moving case when an end surface of the female screw is pressed onto the brake shoe;
• and
• a spring element disposed in the moving case for pressing the female screw via the bearing in the axis direction so that an end surface of the female screw is pressed onto the brake shoe in a no load state, wherein
• when the moving case receives a counterforce from a load so that a thrust generated on the female screw becomes larger than a restoring force of the spring element, the female screw moves in the axis direction with respect to the moving case so that the end surface separates from the brake shoe, and that the restraint of relative rotation of the female screw with respect to the moving case is released, and that the feed screw and the female screw rotate in a differential manner.