Development of a
Blind Rivet Nut Setting Unit
Brief Video
Project Overview
This project focused on the development of an automated blind rivet nut setting unit (BMSE) designed as an end‑of‑arm tool for industrial robots. The goal was to enable fully automated, reliable, and quality‑controlled installation of blind rivet nuts in thin sheet metal components—an operation that is still largely performed manually in high‑volume automotive production.
Figure 1. Finalized robotic tool design featuring the integrated high-precision vision system and electromechanical drive assembly.
The system was developed in cooperation with MSA Vorrichtungsbau GmbH as part of an industrial innovation project and combines mechanical design, drive technology, machine vision, and process monitoring into a single mechatronic solution.
Motivation and Problem Statement
Blind rivet nuts offer a fast and robust method for creating load‑bearing threads in thin sheet components. However, despite their technical advantages, they are rarely automated in large‑scale production. The main reasons are:
- Manual installation is physically demanding and unsuitable for high cycle counts.
Existing robotic solutions on the market are complex, maintenance‑intensive, and limited in process monitoring. - Large component tolerances (up to ±2.5 mm in automotive body parts) complicate precise robotic positioning.
- Quality assurance is often missing, meaning failed set operations are detected too late or not at all.
This project aims to close this gap by developing a compact, robot‑compatible blind rivet nut tool that can correct positional errors autonomously and verify the quality of each set operation in real time.
System Architecture
The developed unit consists of three integrated subsystems:
- Drive System – responsible for picking up, setting, and releasing blind rivet nuts
- Optical Measurement System – determines the exact position of sheet metal holes and compensates tolerances
- Process Verification System – detects faulty setting processes using sensor data
All subsystems are coordinated via an industrial Siemens PLC, ensuring robustness and compatibility with existing automation environments.
Drive and Mechanical Design
The core of the system is a fully electromechanical drive concept, selected through structured design evaluations. The unit is capable of processing blind rivet nuts up to size M10 (steel, aluminum, stainless steel) and generating set forces up to 22 kN.
Two mechanical layouts were developed and evaluated. The final design uses externally mounted drives, resulting in lower weight, improved cooling, easier assembly, and better accessibility.
Figure 2. Final CAD Model of the chosen mechanical layout.
Key design highlights include:
- Servo‑driven ball screw mechanism with a two‑stage gear reduction
- Optimized kinematics enabling a full setting cycle in under 6 seconds
- Compact and lightweight design (≈ 7.2 kg, well below the 10 kg target)
- Use of a standard DIN hex screw as the pulling mandrel, simplifying maintenance and replacement
- FEM‑based structural validation for static and cyclic loads, targeting 300,000 setting cycles
Optical Measurement and Position Correction
To handle component tolerances of up to ±2.5 mm, an optical hole detection system was integrated into the tool.
A 2D machine vision approach was selected, as the setting task is planar and does not require depth information. After evaluating different concepts, a Cognex In‑Sight 7802 camera was chosen for the prototype phase and validated experimentally.
Figure 3. Experimental setup of the optical measurement system used to detect hole positions and compensate part tolerances of up to ±2.5 mm.
The camera system is capable of:
- Detecting hole centers within the robot’s working area
- Achieving a positioning accuracy better than ±0.5 mm
- Distinguishing between empty holes and already set rivet nuts
The measured coordinates are used to correct the robot trajectory before the setting operation begins, enabling reliable processing even on geometrically inaccurate parts.
Process Verification and Quality Monitoring
A key innovation of the project is the integrated process verification system, which classifies each setting operation as OK or Not OK.
Two independent monitoring methods were developed and combined:
- Force and displacement analysis:
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- Set force and stroke are reconstructed from motor torque and encoder data
- Characteristic force‑stroke curves are used to detect under‑setting, over‑setting, and mechanical issues
- Vibration analysis
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- Low‑cost piezo sensors capture structural vibrations during the setting process
- A Raspberry Pi performs FFT‑based frequency analysis and RMS evaluation
- Certain vibration patterns are linked to tool wear or defective rivet nuts
While force‑based monitoring proved reliable for all tested failure scenarios, vibration analysis provided additional redundancy and early error detection in specific cases.
Validation and Results
The complete system was manufactured, assembled, programmed, and experimentally validated.
Key results include:
- Successful automated installation of M10 steel blind rivet nuts
- Reliable force generation and repeatable cycle times
- Accurate optical position correction for misaligned holes
- Clear differentiation between valid and faulty setting processes
- All main functional and non‑functional requirements met or exceeded
Some long‑term metrics, such as endurance testing up to 300,000 cycles, were analytically validated and partially tested, with further testing planned as follow‑up work.
Outcome and Contribution
The project demonstrates a compact, robust, and Industry‑4.0‑ready robotic tool for blind rivet nut installation that:
- Closes a real industrial automation gap
- Combines mechanical engineering, control engineering, machine vision, and signal processing
- Shows that reliable process monitoring can be achieved even with cost‑efficient sensor technology
Beyond its industrial relevance, the work contributes methodological approaches for mechatronic system design, sensor fusion, and in‑process quality assurance, providing a strong foundation for future product development and research.