Cable Actuator Helical Pulleys Joint Clearance
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Solution Overview
Problem
Cable actuators face limitations in increasing joint movement without increasing the overall size, as existing designs either require a larger radius for winding, leading to misalignment and transverse forces, or necessitate a larger overall size due to the projection of the screw on either side of the actuator.
Innovation Solution
A cable actuator design featuring two symmetrically extended cables wound onto pulleys with helical grooves oriented in opposite directions, maintaining a constant winding radius and canceling lateral forces, while allowing increased joint movement with a compact overall size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the cable is wound onto a pulley with a constant primitive radius, then the winding radius remains constant, but the cable becomes progressively misaligned as it is wound, generating transverse forces that interfere with the screw/nut assembly
Solution Approach 1:
The patent employs two pulleys with asymmetric helical grooves that extend in opposite directions. This asymmetric configuration allows each pulley to compensate for the misalignment generated by the other, maintaining constant winding radius while canceling out transverse forces through symmetry of the asymmetric elements.
2Ease of operation
If the screw is allowed to project on either side of the actuator to accommodate cable coupling, then the cable can be coupled to the moving screw, but the overall size of the actuator increases to at least 2C+L
Solution Approach 1:
Instead of coupling the cable to the moving screw as in conventional designs, the patent inverts the approach by coupling the cable to the stationary nut through pulleys mounted on a rotary shaft. This inversion allows the screw to remain compact while the nut handles the cable coupling, reducing the overall actuator size to C+L.
3Length of moving object
If the pulleys are positioned to accommodate increased joint movement, then the joint clearance is increased, but the overall size of the actuator increases
Solution Approach 1:
The patent nests the pulleys and rotary shaft within the existing actuator structure, positioning them such that they utilize the available space efficiently. The pulleys are mounted on the rotary shaft which is integrated into the actuator body, allowing increased joint movement without proportionally increasing the overall actuator dimensions.
Data Source
AI summary
A cable actuator comprising a chassis (1), a screw (2) rotatably mounted on the chassis and driven by an electric motor, a nut (4) that engages with the screw and is combined with anti-rotation means such that rotation of the screw under the action of the motor causes an axial displacement of the nut, two cables (10) coupled to the nut on either side of same, the two cables being wound onto respective joint pulleys (11) each rigidly connected to a same joint shaft (12) and in which the joint pulleys have a helical groove, the helical grooves of the pulleys extending in opposing directions.