Ball Screw Locking via Pawl and Tooth Disc Engagement
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Solution Overview
Problem
Standard friction braking systems for ball screws in industrial lift applications are prone to failure, leading to uncontrolled movement of machines when power is off, as they rely on friction to maintain position, which can result in safety hazards and equipment damage.
Innovation Solution
A ball screw locking apparatus with defined tooth disc and pawl housings that interconnect to facilitate interoperation, where pawls are supported by guides to ensure engagement with the tooth disc, preventing rotation of the ball screw without relying on friction, thus maintaining the machine's position securely.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If friction braking systems are used to hold the ball screw in position, then the device complexity is reduced, but the reliability deteriorates due to friction loss causing uncontrolled movement
Solution Approach 1:
The patent replaces the friction-based mechanical braking system with a positive mechanical locking system using pawls and toothed discs. This substitution eliminates reliance on friction by using geometric interlocking between the pawl teeth and disc teeth, providing reliable position holding through mechanical engagement rather than friction forces.
Solution Approach 2:
The locking system is divided into multiple independent pawls (typically two or more) that can engage with the toothed disc at different positions. This segmentation provides redundancy, as the failure of one pawl does not compromise the overall locking reliability, and allows the system to maintain position holding capability through multiple engagement points.
2Reliability
If multiple redundant brakes are employed to hold the machine, then the reliability improves, but the device complexity increases
Solution Approach 1:
The pawl mechanism automatically engages with the toothed disc through spring-loaded or gravity-assisted action, providing self-activating locking without requiring additional control systems or complex actuation mechanisms. The system uses the inherent forces in the mechanism (spring pressure, gravity) to maintain engagement, eliminating the need for powered brake actuators and control electronics.
3Ease of operation
If pawls are allowed to move freely in the pawl housing, then the ease of operation improves, but the reliability deteriorates as pawls may be forced out of position
Solution Approach 1:
Guide members are introduced as intermediary components between the pawls and the pawl housing. These guides constrain the pawls to move only along predetermined paths, preventing lateral displacement or rotation that could cause disengagement, while still allowing the necessary up-and-down movement for engagement and disengagement operations.
Data Source
AI summary
An apparatus for positively locking a ball screw in a lift position is described. The apparatus includes defined tooth disc and pawl housings, which interconnect to facilitate interoperation of locking components. A tooth disc is secured to the ball screw and actuators associated with each pawl can exert a downward force on each pawl, in order to force the pawls into engagement with the tooth disc via movement in a vertical plane. Owing to the shape, size and positioning of the pawl and tooth disc components relative to one another, and the vertical movement of the pawl members into engagement with the tooth disc, the apparatus of the present invention is capable of locking the hall screw in position at any point along the length of the ball screw, even if the pawls are out of alignment with the teeth, or recesses between adjacent teeth.