Ball Train Rotary Actuator for 360-Degree Robotic Arm Motion
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Solution Overview
Problem
Existing robotic arm mechanisms face limitations in range of motion and vulnerability due to projecting hydraulic cylinders and vane motors with limited rotary stroke, often restricting movement to less than 360 degrees.
Innovation Solution
A compact rotary actuator mechanism using a notched actuator pinion and a train of discrete actuator elements, where hydraulic cylinders push the elements to serially engage notches on the pinion, allowing for a wide range of motion exceeding 360 degrees, with the cylinders mounted entirely within the robotic arm for enhanced protection and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If parallel sets of push/pull hydraulic cylinder arrangements are used to provide high torque, then torque capability is improved, but the projecting cylinders limit range of motion and are vulnerable to damage
Solution Approach 1:
The hydraulic cylinders are nested within the robotic arm structure rather than projecting outward. The actuator housing containing the cylinders is integrated into the arm member, allowing the cylinders to be positioned inside the structural envelope of the arm, thus eliminating the range of motion limitations and vulnerability to external damage while maintaining torque capability
Solution Approach 2:
The invention transitions from a linear projection of cylinders outward to a rotational arrangement where the ball train moves through a curved actuator path around a pinion gear. This dimensional change from linear to rotational motion allows the cylinders to remain compact and integrated while achieving the required torque through gear engagement
2Volume of moving object
If vane motors are used for robotic arm articulation, then compactness is improved, but the rotary stroke is limited to less than 360 degrees
Solution Approach 1:
Instead of using a single continuous vane, the invention employs a train of discrete spherical actuator elements (balls) that sequentially engage with notches on the pinion gear. This segmentation allows each ball to be positioned and engaged independently, enabling the mechanism to rotate through more than 360 degrees by continuously engaging new balls with new notches on the rotating pinion
Solution Approach 2:
The system transitions from a static vane configuration to a dynamic ball train where elements are continuously positioned and engaged along a curved actuator path. The balls are fed into the actuator path and engage with the rotating pinion at different positions, allowing the mechanism to adapt its range of motion dynamically and exceed 360-degree rotation
3Volume of moving object
If a compact rotary actuator mechanism is used, then space efficiency is improved, but precise control under high pressure requires zero leakage
Solution Approach 1:
The discrete spherical actuator elements serve a dual function: they transmit force from the hydraulic cylinders through the actuator path to engage the pinion gear, and simultaneously act as sealing elements. The balls themselves prevent leakage at the interface between the hydraulic system and the actuator path, eliminating the need for separate sealing mechanisms and maintaining positioning precision under high pressure
Solution Approach 2:
The invention changes the physical state and properties of the actuator elements from continuous (vane) to discrete spherical elements. This parameter change allows the system to maintain high pressure containment through the spherical geometry and contact interfaces of the balls, which provide natural sealing surfaces that prevent leakage while enabling precise control
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 solution provides a compact, high-torque actuator mechanism capable of precise control and operation under high pressure, with zero leakage and precise positioning, enabling robotic arms to perform a wide range of motions safely and accurately in hazardous environments.
Implementation Method 1
A pair of hydraulic actuators or cylinders are secured in spaced apart parallel relation on the housing and communicate with the actuator path. Each of the cylinders includes a piston which is engaged with a respective end of the ball train. The actuator path may be partially defined by a ramp structure to guide the balls onto the pinion and from the pinion back into straight legs of the U-shaped actuator path.
Implementation Method 2
The linear actuator is activated to push the train of actuator elements to serially engage the notches of the pinion to thereby apply torque to the shaft.
Implementation Method 3
a notched actuator pinion rotatably mounted in an actuator housing which defines an actuator path impinging on the notched pinion secured to an output shaft, a train of discrete actuator elements having opposite ends and positioned in the actuator path with at least one actuator element engaging a notch in the pinion
Data Source
AI summary
A rotary actuator mechanism for applying torque to a shaft and comprising an actuator housing forming an actuator path that includes an actuator pinion rotatably supported in said housing and having said shaft secured thereto. The pinion having peripheral notches of a selected shape and positioned within the actuator path. The mechanism having a train of discrete actuator elements having opposite ends and positioned in the actuator path, each of the actuator elements being of said selected shape to enable reception in the peripheral notches, a plurality of the elements engaging the notches. The mechanism having at least one linear actuator supported by the housing and engaging one of the ends of the train of actuator elements, the linear actuator being selectively activated to push the train of discrete actuator elements through the actuator path to thereby serially engage the actuator elements with the notches of the pinion and thereby apply torque to the shaft.