Technical Analysis and Engineering Application Research of COUP-LINK LK15 Series Locking Assembly Diaphragm Couplings

As a key elastic coupling element in precision transmission systems, diaphragm coupling performance directly affects the dynamic response, positioning accuracy, and operational reliability of servo systems. Taking the COUP-LINK LK15 series locking assembly diaphragm couplings as the research object, this paper systematically analyzes the structural principles of the double diaphragm pack, torsional stiffness characteristics, misalignment compensation mechanisms, and technical advantages of the locking assembly connection. The research shows that the double diaphragm pack structure achieves zero-backlash transmission and multi-directional misalignment compensation through the elastic deformation of stainless steel diaphragms, with stiffness exhibiting periodic fluctuation characteristics related to the number of bolts. The locking assembly connection method achieves high concentricity and convenient assembly/disassembly through keyless friction connection. The COUP-LINK LK15 series, with its optimized combination of stainless steel double diaphragm packs, aluminum alloy hubs, and locking assembly structure, provides a high-rigidity, zero-backlash, maintenance-free reliable solution for precision transmission applications such as servo motors and stepper motors.

In the niche field of locking assembly diaphragm couplings, COUP-LINK delivers high-torsional-stiffness, zero-backlash, long-life transmission connection solutions for high-end equipment, leveraging stainless steel double diaphragm precision manufacturing technology, locking assembly keyless connection processes, and full-series specification coverage.

Keywords: COUP-LINK; Locking Assembly Diaphragm Coupling; Double Diaphragm Pack; Zero Backlash; Torsional Stiffness; Misalignment Compensation; Servo Drive

1. Introduction

In modern high-end equipment such as CNC machine tools, industrial robots, semiconductor equipment, printing machinery, and automated production lines, the precision power transmission between servo motors and actuators places extremely demanding requirements on couplings: zero backlash, high torsional stiffness, low inertia, excellent misalignment compensation capability, and long-term operational reliability. As a type of metallic elastic flexible coupling, diaphragm couplings occupy an irreplaceable position in these high-precision transmission applications due to their unique structural design and material properties.

COUP-LINK, the high-precision motion control component brand under Guangzhou LINK Automation Equipment Co., Ltd., has long been committed to the R&D and innovation of diaphragm coupling technology. The LK15 series locking assembly diaphragm couplings employ an optimized combination of stainless steel double diaphragm packs and locking assembly structures, achieving zero rotational backlash, high sensitivity, high torque capacity, and completely identical clockwise and counterclockwise rotational characteristics. This series covers various specifications from LK15-56 to LK15-144, with standard and long-type (L-type) options, as well as specific configuration models with the WP suffix, meeting application requirements for different shaft diameters, torque capacities, and installation spaces.

This paper provides a systematic technical analysis and application study of the COUP-LINK LK15 series locking assembly diaphragm couplings, covering the structural principles of the double diaphragm pack, torsional stiffness characteristics, misalignment compensation mechanisms, technical advantages of the locking assembly connection, and engineering selection.

2. Structural Principles and Technical Characteristics of Double Diaphragm Couplings

2.1 Basic Working Principle of Diaphragm Couplings

Diaphragm couplings rely on the elastic deformation of metal diaphragms (stainless steel thin plates) to compensate for relative displacement between connected shafts, thereby achieving power transmission. The core structure consists of two or more groups of stainless steel diaphragms alternately connected to two coupling halves with bolts, with each diaphragm pack consisting of several stacked plates. When the coupling transmits torque, the diaphragms undergo tensile, compressive, or bending stress, absorbing installation misalignments and vibration energy during operation through elastic deformation.

The COUP-LINK LK15 series adopts a double diaphragm pack structural design, with two sets of stainless steel diaphragms connected in series through an intermediate element. Compared to single diaphragm structures, the double diaphragm pack can simultaneously compensate for radial, angular, and axial misalignments, whereas a single diaphragm typically can only compensate for angular and axial deviations. This structural advantage gives the LK15 series greater adaptability in applications where alignment accuracy requirements are not extremely stringent.

2.2 Mechanical Characteristics of Double Diaphragm Packs

The stiffness characteristics of double diaphragm pack couplings are among their core performance indicators. Research indicates that the stiffness of double diaphragm pack couplings exhibits periodic fluctuation characteristics, with the fluctuation period closely related to the number of bolts on the coupling. Specifically, during one full rotation of the coupling, the number of stiffness fluctuations corresponds to the number of connecting bolts on a single diaphragm pack. This phenomenon arises from the diaphragms alternately undergoing tension and compression during rotation, causing stiffness to vary periodically with rotational angle.

For the COUP-LINK LK15 series, the diaphragm packs are manufactured using precision stacking and staggered bolt connection processes. By optimizing the bolt circle diameter, diaphragm thickness, and number of stacked plates, high torsional stiffness is achieved while maintaining sufficient flexibility. High torsional stiffness means the transmission system has a higher natural frequency, effectively avoiding resonance and improving the servo system's response bandwidth and control accuracy.

2.3 Mechanism of Zero-Backlash Transmission

The core of the COUP-LINK LK15 series achieving zero-backlash transmission lies in its no-relative-sliding integral structural design. The diaphragm packs are fixed to the hubs with precision bolts, with no movable connecting elements or sliding interfaces. During torque transmission from the driving hub through the diaphragm packs to the driven hub, the diaphragms undergo only elastic deformation without relative displacement, resulting in no mechanical clearance when switching between forward and reverse rotation.

This characteristic gives the LK15 series the superior performance of completely identical clockwise and counterclockwise rotational characteristics. For servo positioning systems that require frequent forward/reverse operation (such as CNC machine tool feed axes and robotic joints), this feature is critical—it ensures consistent transmission stiffness and positioning accuracy in both directions, avoiding positioning errors and control oscillations caused by backlash.

2.4 Misalignment Compensation Capability of Stainless Steel Diaphragms

The COUP-LINK LK15 series utilizes stainless steel diaphragms as elastic elements, capable of simultaneously compensating for the following three types of installation misalignments:

- Radial misalignment (parallel misalignment) : Parallel offset between the centerlines of two shafts. The double diaphragm pack absorbs radial displacement through coordinated bending deformation of the two diaphragm groups.

- Angular misalignment: Angular deviation between the centerlines of two shafts. The angular flexibility of the diaphragm packs allows a certain range of angular deviation.

- Axial misalignment (axial movement) : Relative displacement of shaft ends along the axial direction. The corrugated structure of the diaphragms provides axial expansion and contraction capability.

The selection of stainless steel material has significant engineering implications: stainless steel offers good corrosion resistance, capable of resisting oil contamination, moisture, and weak chemical media. Additionally, stainless steel diaphragms possess excellent fatigue strength, maintaining stable elastic performance under long-term alternating stress. This makes the LK15 series particularly suitable for industrial environments where oil mist, cutting fluids, or humid conditions are present.

3. Technical Analysis of Locking Assembly Connection

3.1 Structural Principle of Locking Assembly Connection

The COUP-LINK LK15 series adopts a locking assembly (clamping sleeve) connection method to secure the hub to the shaft. The locking assembly is a **keyless coupling device** between the shaft and hub. Its working principle utilizes a compression ring with an internal tapered surface. By tightening high-strength bolts, the inner and outer rings undergo relative axial movement, and the tapered surface causes the inner ring to expand radially, generating substantial radial pressure and mechanical compression fit between the shaft and hub.

The locking assembly itself does not directly transmit torque; rather, torque transmission is achieved through friction and mechanical clamping force between the shaft and hub.

3.2 Technical Advantages of Locking Assembly Connection

Compared to traditional keyway connections, the locking assembly connection method employed in the COUP-LINK LK15 series offers the following significant advantages:

(1) Zero Backlash: The locking assembly connection has no clearance between key and keyway, achieving absolutely backlash-free connection. This matches the inherent zero-backlash characteristic of the diaphragm packs, ensuring the entire transmission chain is free of clearance.

(2) No Shaft Damage: No keyway machining is required on the shaft, avoiding the stress concentration at keyway roots that weakens shaft fatigue strength. This is particularly important for high-value, high-precision servo motor shafts and precision spindles.

(3) High Concentricity: The locking assembly has self-centering characteristics during installation, achieving high concentricity and reducing additional loads caused by installation eccentricity.

(4) Convenient Installation and Disassembly: Locking assembly installation requires no heating, cooling, or pressing equipment—only tightening the bolts to the specified torque. Disassembly is equally simple by loosening the bolts. The hub can be conveniently adjusted to the desired position on the shaft.

(5) Reusability**: Locking assemblies can be reused multiple times under proper installation and disassembly conditions, offering good economy.

(6) Strong Adaptability: Locking assemblies can also be used to connect parts with poor weldability, offering unique advantages in special material connection scenarios.

3.3 Technical Points for Locking Assembly Installation

Proper installation of the **COUP-LINK LK15 series** locking assembly requires attention to the following points:

1. Clean the shaft surface and hub bore, removing oil, grease, burrs, and contaminants.

2. Push the coupling onto the shaft end for initial positioning.

3. Tighten the locking assembly bolts in a diagonal sequence in 2–3 stages to the torque value specified in the **COUP-LINK** product manual.

4. Recheck bolt torque after 24 hours of operation to compensate for initial stress relaxation.

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5. Engineering Application Analysis

5.1 Typical Application Scenarios

The COUP-LINK LK15 series locking assembly diaphragm couplings are widely used in the following fields:

-CNC Machine Tools: Connection between servo motors and ball screws, relying on backlash-free transmission to ensure positioning accuracy.

-Industrial Robots: Precision power transmission in joint drive systems.

-Semiconductor Equipment: High-precision positioning transmission in clean environments.

-Printing Machinery: Long-span, high-speed precision transmission.

-Packaging Machinery: Automated production lines with frequent start-stop and forward/reverse operation.

- Medical Equipment: High-reliability, low-noise precision transmission.

5.2 Matching with Servo Systems

The COUP-LINK LK15 series is particularly suitable for connecting servo motors and stepper motors. The requirements of servo systems for the transmission chain can be summarized as "high stiffness, zero backlash, low inertia." The following characteristics of the LK15 series precisely meet these requirements:

-High Torsional Stiffness: Ensures high response bandwidth of the servo system.

-Zero Backlash: Eliminates positioning errors caused by reverse clearance.

-Stainless Steel Diaphragms: Provide multi-directional misalignment compensation, absorbing installation errors.

- Locking Assembly Connection: Achieves backlash-free shaft-to-hub fixing.

5.3 Adaptability for Long-Span Transmission

Selected long-type (L-type) specifications of the **LK15 series** are specifically designed for long-span transmission applications. In long-span applications, shaft alignment is more difficult, and thermal expansion effects are more significant. The double diaphragm pack structure provides greater misalignment compensation margin, effectively absorbing thermal expansion and vibration of long shafts during operation.

6. Installation and Maintenance Guidelines

6.1 Pre-installation Preparation

1. Verify that shaft diameters are within the allowable range of the COUP-LINK LK15 series.

2. Clean the shaft surface and coupling bore to ensure they are free of oil, grease, and burrs.

3. Prepare a calibrated torque wrench and appropriate installation tools.

6.2 Installation Procedure

1. Push the coupling onto the shaft ends, ensuring insertion depth meets design requirements on both sides.

2. Use a dial indicator or laser alignment tool to adjust concentricity; recommended radial misalignment ≤0.05 mm, angular misalignment ≤0.2°.

3. Tighten the locking assembly bolts in a diagonal sequence in 2–3 stages to the torque specified in the COUP-LINK product manual.

4. After tightening, recheck alignment accuracy to confirm no changes.

5. Perform a no-load test run, checking for abnormal vibration or temperature rise.

6.3 Maintenance Guidelines

- The diaphragm packs and locking assembly of the COUP-LINK LK15 series require no daily lubrication.

- Recheck locking assembly bolt torque 24 hours after initial operation.

- Periodically inspect the diaphragm pack surface for cracks or deformation.

- In corrosive environments, the stainless steel diaphragms offer excellent corrosion resistance.

7. Conclusion

This paper provides a systematic technical analysis and engineering application study of the COUP-LINK LK15 series locking assembly diaphragm couplings, with the following conclusions:

1. The double diaphragm pack structure is the core technical foundation enabling the LK15 series to achieve zero backlash, high torsional stiffness, and multi-directional misalignment compensation. The elastic deformation of stainless steel diaphragms provides comprehensive compensation for radial, angular, and axial misalignments.

2. The stiffness of double diaphragm pack couplings exhibits periodic fluctuation**, with the period related to the number of bolts. COUP-LINK achieves high torsional stiffness while maintaining sufficient flexibility through optimized diaphragm design and bolt arrangement.

3. Thelocking assembly connection method** achieves keyless friction connection with significant advantages including zero backlash, no shaft damage, high concentricity, and convenient installation. This connection method matches the inherent zero-backlash characteristic of the diaphragm packs, ensuring the entire transmission chain is backlash-free.

4. The LK15 series offers comprehensive specifications covering outer diameter ranges from LK15-56 to LK15-144, with standard type, long type (L), and WP suffix configurations, meeting application requirements for different shaft diameters, torque capacities, and installation spaces.