Cable Actuator Pulley Layout for Compact Linear Travel
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Solution Overview
Problem
Existing cable actuators are unsuitable for producing very compact miniaturized actuators due to their bulkiness in width and height, despite having advantageous characteristics in terms of force delivery and linearity.
Innovation Solution
A cable actuator design utilizing a single pair of return mechanisms, a carriage connected to the nut via cables, and a prismatic linear guidance mechanism to reduce width and total length, with optional features like notched belts and tensioning devices to enhance compactness and reduce friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two pairs of pulleys are placed on either side of the screw with strands in the same plane, then force balance and friction reduction are improved, but width and height bulk increase
Solution Approach 1:
The patent transitions from a two-dimensional arrangement (two pairs of pulleys in the same plane) to a three-dimensional configuration (single pair of pulleys with cables extending in different directions). The first cable extends in a first direction while the second cable extends in a second direction different from the first, utilizing spatial dimensionality to achieve force balance without increasing width.
2Length of moving object
If the total length is reduced to close to maximum travel, then compactness improves, but height bulk increases due to pulley positioning
Solution Approach 1:
The patent reduces total length to close to maximum travel by repositioning the pulley assembly and utilizing three-dimensional cable routing. The height bulk is managed by allowing cables to extend in different directions from the pulley, with the second cable extending in a direction different from the first, effectively distributing spatial requirements.
3Volume of moving object
If a motorised nut design is used, then width is reduced, but total length increases to twice the maximum travel
Solution Approach 1:
The patent inverts the conventional motorised nut design by placing the motorised screw instead at one end of the actuator, with the nut engaging the screw and moving along its longitudinal axis. This inversion allows the nut to be connected via cables to a pulley assembly that provides mechanical advantage, achieving compact total length close to maximum travel while maintaining reduced width.
4Force
If the nut is connected via cables to a pulley assembly, then force delivery improves, but device complexity increases
Solution Approach 1:
The pulley assembly serves multiple functions: it provides mechanical advantage for force delivery, guides the cables in different directions, and enables compact packaging of the actuator. The first and second cables both engage the pulley assembly, with the pulley structure facilitating force transmission while maintaining a relatively simple overall device architecture.
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
The design achieves a reduced width and total length close to the maximum travel of the nut, minimizing parasitic kinematic oscillations and friction, thereby improving the compactness of the actuator.
Implementation Method 1
a screw/nut assembly comprising a nut (4) engaging with a screw (2) extending along a longitudinal axis (Ox)
Implementation Method 2
A first cable (6), the ends of which are connected to the nut (4), makes a first loop between a first pulley (10) and a second pulley (11)
Data Source
AI summary
An actuator includes a frame, a screw/nut assembly including a nut which engages with a screw extending along a longitudinal axis, a motor arranged to rotate the screw and bring about a linear movement of the nut, the actuator further includes a single pair of return mechanisms having a first return mechanism and a second return mechanism which are rotatably mounted on the frame, the first return mechanism being connected to an output of the actuator, a first transmission member for transmitting a pulling force connected to the nut by its first end and its second end, which transmission member engages with the first return mechanism and the second return mechanism, and an anti-rotation device for preventing the nut from rotating relative to the screw.