An actuator includes a casing, an output disc, a transmission component, a cable, a power source, and a tension adjustment assembly. The output disc and the transmission component are rotatably disposed on the casing. The cable is disposed through the transmission component and connected to the output disc. The power source can drive the transmission component. The tension adjustment assembly includes a lever, an elastic component, and a slidable component. The lever has a first end and a second end opposite to each other. The first end is connected to the cable. The elastic component is connected to the casing and the second end of the lever. The slidable component is in contact with a portion of the lever located between the first end and the second end, and is slidable along the lever to change its position to adjust a tension of the cable.

An actuator includes a casing, an output disc, a transmission component, a cable, a power source, and a tension adjustment assembly. The output disc and the transmission component are rotatably disposed on the casing. The cable is disposed through the transmission component and connected to the output disc. The power source can drive the transmission component. The tension adjustment assembly includes a lever, an elastic component, and a slidable component. The lever has a first end and a second end opposite to each other. The first end is connected to the cable. The elastic component is connected to the casing and the second end of the lever. The slidable component is in contact with a portion of the lever located between the first end and the second end, and is slidable along the lever to change its position to adjust a tension of the cable.

In one embodiment, a selectable-rate spring comprises a flexure bar connected to a rotatable shaft, the flexure bar having at least one arched portion. The selectable-rate spring also includes at least one rotational contactor connectable to a link member, wherein the rotational contactor rotates about an axis while maintaining contact with the arched portion of the flexure bar. As the rotational contactor rotates, it changes the connection stiffness between the rotatable shaft and the link member.

In one embodiment, a selectable-rate spring comprises a flexure bar connected to a rotatable shaft, the flexure bar having at least one arched portion. The selectable-rate spring also includes at least one rotational contactor connectable to a link member, wherein the rotational contactor rotates about an axis while maintaining contact with the arched portion of the flexure bar. As the rotational contactor rotates, it changes the connection stiffness between the rotatable shaft and the link member.

A torque disc comprising a fixing surface and at least one restraining element. The fixing surface defines an area of the torque disc for attachment to a fastener in use, and the at least one restraining element extends from the fixing surface so as to engage in use with at least one portion of the fastener to restrain rotational movement of the fastener during attachment to or detachment from the torque disc.

A torque disc comprising a fixing surface and at least one restraining element. The fixing surface defines an area of the torque disc for attachment to a fastener in use, and the at least one restraining element extends from the fixing surface so as to engage in use with at least one portion of the fastener to restrain rotational movement of the fastener during attachment to or detachment from the torque disc.

A universal joint assembled in a drill string transfers torque between two components where rotation of the components may not be completely aligned. The universal joint includes upper and lower members with radial teeth connected by a serpentine retainer. As the joint rotates the members can pivot within the confines of the serpentine retainer to accommodate misalignment of the components. Axial force can be transferred through a bearing member between the members.

Apparatus for transmitting motion to a moveable body comprising: a first bar having ends; two articulated arms, each comprising first and second arms connected at a joint having an axis about which the first and second arms rotate, wherein the first arms are of equal length, the second arms are of equal length and the second arm of each articulated arm is connected to a different end of the bar at a joint having an axis about which second arm and bar rotate; a mount connected to the first arm of each articulated arm at a joint having an axis about which first arm rotates; a second bar coupled to each articulated arm at a joint having an axis about which the second bar rotates; and a piezoelectric motor coupled to the first bar controllable to apply a force selectively in either direction along the bar's length; wherein, the joints are configured so that all the axes are substantially parallel and the first arms are parallel and the second arms are parallel for all rotations about the axes.

Apparatus for transmitting motion to a moveable body comprising: a first bar having ends; two articulated arms, each comprising first and second arms connected at a joint having an axis about which the first and second arms rotate, wherein the first arms are of equal length, the second arms are of equal length and the second arm of each articulated arm is connected to a different end of the bar at a joint having an axis about which second arm and bar rotate; a mount connected to the first arm of each articulated arm at a joint having an axis about which first arm rotates; a second bar coupled to each articulated arm at a joint having an axis about which the second bar rotates; and a piezoelectric motor coupled to the first bar controllable to apply a force selectively in either direction along the bar's length; wherein, the joints are configured so that all the axes are substantially parallel and the first arms are parallel and the second arms are parallel for all rotations about the axes.

A universal joint includes a first band and a second band which are separated by a slot, are cylindrical and coaxial with one another with respect to a common axis, and further includes a first torsion bar, whose ends are joined to the first band, and a second torsion bar whose ends are joined to the second band. Such a universal joint thus has a relatively simple structure.