Multi-Leaf Collimator Leaf Rolling Element Bearing Design
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Solution Overview
Problem
Current multi-leaf collimators in radiotherapy limit the speed of leaf movement due to high frictional resistance, which restricts the overall speed of radiotherapy treatments and combined radiotherapy/Computed Tomography arrangements.
Innovation Solution
The use of rolling-element bearings, such as ball races, to support and drive the leaves, reducing frictional resistance and allowing for faster movement by enabling a true rolling motion without sliding, and incorporating a drive motor outside the leaf to minimize frictional losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If leaves are supported on sliding guides or rotatable wheels, then the structure is simple and easy to manufacture, but the frictional resistance is high which limits leaf movement speed
Solution Approach 1:
The patent replaces the sliding friction mechanism with a rolling friction mechanism by introducing ball bearings between the leaves and the guide structure. This substitution of mechanical interaction mode dramatically reduces frictional resistance and enables faster leaf movement speeds.
Solution Approach 2:
The patent changes the physical state of the contact interface from sliding to rolling by introducing spherical rolling elements. This parameter change in the mode of motion transformation fundamentally alters the friction characteristics and enables high-speed operation.
2Productivity
If leaves are moved quickly to increase treatment speed, then productivity increases, but the risk of buckling and jamming increases
Solution Approach 1:
By replacing sliding contact with rolling contact through ball bearings, the system reduces frictional forces that cause buckling and jamming. This allows faster leaf movement speeds to be achieved reliably without increasing the risk of mechanical failure.
Solution Approach 2:
The ball bearing arrangement provides a cushioning effect by distributing loads through multiple spherical contact points, preventing sudden buckling or jamming events even during high-speed operation. The rolling elements absorb and distribute mechanical stresses before they can cause failure.
3Speed
If the drive motor is positioned close to the leaf to drive it directly, then the drive mechanism is compact, but frictional losses increase and limit movement speed
Solution Approach 1:
The patent substitutes direct sliding contact between the drive mechanism and leaf with a rolling element bearing system. This allows the drive motor to be positioned optimally while minimizing frictional losses through the rolling contact interface, enabling faster and more efficient leaf movement.
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 solution significantly increases the speed of leaf movement, reducing the risk of buckling and jamming, enabling faster radiotherapy treatments and quicker gantry rotation.
Implementation Method 1
each leaf is supported by the frame on a bearing comprising a plurality of rolling elements such that the rolling surfaces of the rolling elements contact at least a surface of the frame
Data Source
AI summary
The leaves of a multi-leaf collimator can be driven more easily and hence more quickly if they are supported on a ball-race instead of in a sliding groove. A recirculating path is preferred, in which the rolling elements of the ball-race support the leaf over part of their path and then return to a start of the path. In addition, the rolling elements could be driven by a drive screw in order to drive the leaf.