Linear Actuator Cable Fastening for High Axial Force
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Solution Overview
Problem
Conventional linear actuators face challenges in applying high axial forces and achieving high-speed movement while maintaining a cylindrical rod design, which is hindered by the presence of guide pulleys that misalign traction forces with the sliding direction of the rod.
Innovation Solution
A linear actuator design where the output member is shaped as a rod slidably received in a cylindrical cavity, with cables fastened at axially opposite points relative to the driving pulley, eliminating the need for a third guide pulley and allowing for parallel orientation of the driving pulley axis to reduce overall size or omitting guide pulleys for increased size but maintaining high traction forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a third guide pulley is used to prevent the output member from being a rod, then the structural integrity is maintained, but the device complexity increases and the rod cannot be made as a simple cylindrical component
Solution Approach 1:
The patent removes the third guide pulley from the system by repositioning the cable fastening points to axially opposite sides of the output member. This extraction eliminates the problematic component while maintaining structural integrity through the alternative cable arrangement.
Solution Approach 2:
Instead of using a third guide pulley to redirect cables, the invention inverts the approach by fastening cables at axially opposite points on the output member itself. This reversal of the conventional cable routing method achieves the same structural support function without the additional pulley.
2Area of stationary object
If the driving pulley axis is oriented parallel to the axial direction, then the transverse size is reduced, but the cable routing becomes more complex requiring guide pulleys
Solution Approach 1:
The patent utilizes the axial dimension by fastening cables at axially opposite points on the output member. This dimensional approach allows the driving pulley axis to be oriented parallel to the axial direction, reducing transverse size while the axial cable fastening compensates for the routing complexity.
3Device complexity
If the driving pulley axis is oriented perpendicular to the axial direction, then guide pulleys can be omitted, but the transverse size of the actuator increases
Solution Approach 1:
The patent introduces asymmetry in the cable fastening arrangement by positioning fastening points at axially opposite locations rather than symmetrically on the same side. This asymmetric configuration enables the driving pulley axis to be perpendicular to the axial direction, simplifying cable routing while managing the transverse size increase.
4Power
If cables are fastened at axially opposite points, then high axial forces and high-speed movement are achieved, but the cable tension alignment becomes more critical
Solution Approach 1:
The patent applies local quality by specifically designing the cable fastening points at axially opposite locations on the output member. This localized configuration optimizes force transmission in the axial direction, achieving high axial forces and speeds while the precise opposite positioning inherently manages the alignment requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the application of high axial forces and high-speed movement of the rod in a reversible manner, suitable for cylindrical applications, and reduces the transverse size of the actuator by aligning traction forces with the sliding direction, enhancing its usability in various applications including robotic rehabilitation systems.
Implementation Method 1
an electric motor (or gear motor) and a motion conversion mechanism for converting the rotary motion produced by the electric motor
Implementation Method 2
a driving pulley set into rotation by the electric motor and a cable, or similar elongated mechanical transmission member, which is wound onto the driving pulley
Data Source
AI summary
An actuator (10) includes a body (12), an output member (14) slidably received in the body (12) along— a first axis (X1), an electric motor (18) arranged to set into rotation a motor shaft (20) about a, second axis (X2) and a motion conversion mechanism (22) for converting the rotary motion produced by the electric motor (18) about the second axis (X2) into a translational motion of the output member (14) along the first axis (X1). The motion conversion mechanism (22) includes a driving pulley (24) which is drivingly connected for rotation with the motor shaft (20) and an elongated mechanical transmission member which is wound onto the driving pulley (24) and is fastened at its two opposite ends to the output member (14) to draw this latter in either direction along the first axis (X1) as a result of the rotation of the driving pulley (24) in either direction. The output member (14) is shaped as a rod and is received in a cylindrical cavity (16) of the body (12) so as to project partially therefrom. The elongated mechanical transmission member (2S) is fastened to the output member (14) at axially opposite points of this latter with respect to the driving pulley (24).