EK series ball screw end support

"EK" typically refers to another structural form of the ball screw fixed-end support unit, specifically denoting an "eccentric locking collar type" fixed-side support unit. It is functionally identical to BK (fixed end)—both withstand bidirectional axial forces and fix the axial position of the screw—but differs fundamentally in the method of locking the screw shaft.

Introduction

I. Core Positioning and Nomenclature

Positioning: A ball screw fixed-side support unit that uses an eccentric locking collar for fixation. It is a fixed-end solution that does not require a shaft shoulder or locknut.

Nomenclature Interpretation:

E: Typically stands for "Eccentric," referring to its core locking principle.
K: Same as in BK, stands for "Fixed."

Core Value: Provides a simple, reliable, and high-rigidity fixed-end support solution for screw shafts without machined shoulders, particularly suitable for space-constrained applications or situations where simplifying shaft end machining is desired.

II. Core Structure and Locking Principle

The EK unit is identical to the BK unit in the bearing section (typically using paired angular contact ball bearings). The key difference lies in the locking mechanism between the bearing inner ring and the screw shaft:

Eccentric Locking Collar:
This is the core component of the EK unit. It is a precision sleeve with a longitudinal slit. Its inner bore has a precise clearance fit with the screw shaft, and its outer diameter fits the bearing inner bore. The sleeve's outer surface features an eccentric lug or wedge profile.

Locking Ring/Locknut:
A locking ring with an inner conical bore or inner eccentric bore is threaded onto the bearing housing.

Locking Principle (Two-Step Process):

Radial Locking: When the locking ring is tightened, its inner conical surface presses against the eccentric sleeve's lug. Due to the eccentric action, the sleeve undergoes uniform radial elastic deformation, tightly clamping onto the screw shaft.
Axial Positioning: Simultaneously, the clamped eccentric sleeve transmits the axial forces (in either direction) from the screw shaft through the bearing inner ring to the angular contact bearing pair, and ultimately to the bearing housing.

Key Point: EK achieves axial fixation through the high friction generated by radial clamping, eliminating the need for a machined shoulder on the screw shaft, as well as threading the shaft end and installing a locknut.

III. Core Features and Advantages

Suitable for Plain Shafts Without Shoulders:
This is the most prominent advantage of EK. It allows the use of standard-length plain shaft screws, eliminating the need for machining shoulders, relief grooves, and threads, thereby reducing manufacturing cost and complexity of the screw shaft.
Compact Structure, Saves Axial Space:
By eliminating the shoulder and locknut, the screw shaft occupies less axial space within the EK unit, beneficial for shortening the total length of the screw system in compact designs.
Easy Installation and Adjustment:
The screw shaft can be easily inserted into the eccentric sleeve. Fixation is achieved by simply tightening one locking ring, completing radial clamping and axial positioning—a simple and fast assembly process. The axial position of the screw shaft can be continuously adjusted within a certain range (by adjusting the insertion depth), facilitating on-site fine-tuning.
High Rigidity and Reliability:
The clamping force is large and uniform, providing connection rigidity comparable to BK's shoulder-contact method. It reliably transmits high torque and axial forces. It offers good anti-loosening performance and is less prone to loosening in vibrating environments.
Easy Maintenance:
The screw shaft can be disassembled by loosening the locking ring, facilitating maintenance or replacement without removing the entire support unit.

IV. Comparison with BK Fixed End

Feature	EK (Eccentric Locking Fixed End)	BK (Shoulder & Locknut Fixed End)
Screw Shaft End Requirement	Plain shaft is sufficient. No shoulder or threading required.	Must have machined shoulder and threading for bearing contact and locknut tightening.
Locking Principle	Radial friction locking (eccentric sleeve clamping the shaft).	Axial mechanical preload (shoulder contacts bearing + locknut tightening).
Axial Space	More compact, saves space by eliminating shoulder and locknut.	Requires reserved space for shoulder and locknut.
Installation Convenience	Very high. Insert shaft and tighten one ring. Position is adjustable.	Requires ensuring shoulder length and using two wrenches to tighten locknut and lock washer, involving more steps.
Applicability	High versatility, especially suitable for space-constrained designs, standard plain shafts, simplified machining, or scenarios requiring axial position adjustment.	Traditional, classic, most widely used method. Suitable for all applications with sufficient space and screw shafts machined to standard.
Cost	Support unit itself may be slightly more expensive, but screw shaft machining cost is lower.	Support unit may be slightly less expensive, but screw shaft requires additional machining.

V. Typical Application Fields

The EK support unit, due to its flexibility, is suitable for various applications, particularly offering clear advantages in specific scenarios:

Compact linear modules and slides: Where maximizing stroke utilization in space-constrained designs is crucial.
Equipment with strict limitations on screw shaft length: EK allows for longer effective strokes within a fixed total length.
Equipment using standard-length plain shaft screws: Eliminates the need for custom shaft end machining, shortening procurement lead times and reducing costs.
Equipment requiring frequent debugging or screw replacement: Facilitates disassembly and repositioning.
General automation equipment, robotics, medical devices: Seeking design and assembly convenience while meeting performance requirements.

VI. Selection and Usage Guidelines

Confirm Shaft End Form: Clearly determine if the screw shaft is a plain shaft without shoulders. If yes, EK is ideal. If it already has shoulders, BK is more suitable.

Match Shaft Diameter: Strictly select the corresponding EK unit model based on the screw shaft diameter.

Correct Installation:

Ensure the contact area between the screw shaft and eccentric sleeve is clean and smooth, free of burrs and oil contamination.
Tighten the locking ring to the torque specified by the manufacturer to ensure sufficient clamping force, avoiding over-tightening that could damage the eccentric sleeve.
After installation, always manually rotate the screw to check for smooth, unobstructed movement.

Paired Usage: Like BK, EK must be paired with a BF or FK floating end to release thermal stress.

Finalize Axial Position Before Locking: Perform the final locking operation only after definitively determining the axial position of the screw shaft relative to the nut and worktable.

The EK support unit is an important "user-friendly" innovation in fixed-end support technology. Through its ingenious eccentric locking collar design, it shifts the challenge of fixation from "shaft machining" to "support unit design," providing greater convenience and flexibility for equipment designers and assembly engineers. Choosing EK means obtaining a more compact layout, easier installation, and lower screw shaft machining requirements while ensuring performance equivalent to traditional BK. It is a highly valuable option in modern precision equipment design.