Concentric Opposed Cam Actuator for Extended Rotational Motion
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Solution Overview
Problem
Conventional linear-to-rotary actuators with a single helix-shaped end cam are limited to less than 180 degrees of rotational motion due to each piston only acting on half of the cam surface, restricting the range of motion in robotic joints.
Innovation Solution
The use of concentric, nested cams with a piston carrier containing antagonistic pistons that act on both the outer and inner cams at specific points, allowing for greater rotational motion by fixing one end cam and utilizing the helix angles of both cams to produce a gearing effect, while minimizing friction and backlash through a hydraulic 'H-bridge' mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single helix-shaped end cam is used in a linear-to-rotary actuator, then the structure is simple, but the range of rotational motion is limited to less than 180 degrees
Solution Approach 1:
The patent employs nested concentric cams where an inner cam is positioned inside the outer cam, both sharing a common central axis. This nesting arrangement allows the system to achieve greater than 180 degrees of rotational motion while maintaining a compact structure, directly resolving the contradiction between structural simplicity and range of motion.
Solution Approach 2:
The patent transitions from a single-cam design to a multi-cam concentric arrangement, adding dimensional complexity in the radial direction. This allows the system to overcome the 180-degree rotational limitation by utilizing multiple cam surfaces at different radii, enabling the piston to act on both cams sequentially to achieve extended rotation.
2Ease of operation
If concentric nested cams with antagonistic pistons are used, then the range of rotational motion exceeds 180 degrees, but the device complexity increases
Solution Approach 1:
The piston carrier is designed to accommodate multiple antagonistic pistons that can act on different cams, making it a multi-functional component. This universal design allows the same structural element to serve multiple functions in controlling the rotation through different cam surfaces, reducing the need for additional specialized components.
Solution Approach 2:
The patent merges the functions of multiple cams and multiple pistons into a single integrated actuator assembly. The concentric cams are combined in a nested configuration, and the antagonistic pistons are integrated within the same piston carrier, creating a unified mechanism that achieves greater than 180 degrees rotation without requiring separate actuator systems.
3Reliability
If hydraulic H-bridge mechanism is implemented, then friction and backlash are minimized, but the manufacturing precision requirements increase
Solution Approach 1:
The patent employs a hydraulic H-bridge mechanism to actuate the antagonistic pistons. This hydraulic system provides precise control over piston movement, minimizing friction and eliminating backlash in the mechanical transmission. The hydraulic fluid transmission allows for smooth, controlled motion that reduces mechanical wear and improves reliability.
Solution Approach 2:
The cam surfaces are designed with asymmetric profiles and different radii, with the inner cam having a smaller radius than the outer cam. This asymmetric design, combined with inverse alignment, creates specific contact points that optimize the mechanical advantage and control the rotational motion while working in conjunction with the hydraulic actuation system.
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
This design enables a range of rotational motion greater than 180 degrees with low friction and no backlash, optimizing joint performance and packaging length by allowing the outer cam to rotate closer to 360 degrees with half the torque output.
Implementation Method 1
Linear actuation of one of the pistons toward the end cams may cause rotation of at least one of the end cams, and may also cause linear motion of the other piston in a direction away from the end cams
Data Source
AI summary
An example device may include a rounded outer incline ramp and a rounded inner incline ramp surrounding a central axis. The rounded inner incline ramp and the rounded outer incline ramp may be inversely aligned relative to the central axis. The device may also include a piston carrier oriented in a direction parallel to the central axis. The piston carrier may include a first piston including a first roller positioned on the two ramps at a first point, where the first piston is configured to act on the two ramps in a direction parallel to the central axis. The piston carrier may also include a second piston including a second roller positioned on the two ramps at a second point opposite the first point, where the second piston is configured to act on the two ramps in a direction parallel to the central axis.