Modification/improvement of the screwing process based on the analog rangefinder
Case Study created in collaboration with Machine Design Company
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The Balluff Case Study series are articles written by Balluff experts, our company's partners, integrators, and specialists implementing dedicated solutions for manufacturing companies using Balluff tools and solutions.
Automating the screwing process is not easy, it depends on many factors, and the problems start at the thread forming stage. The type of thread outline, its tolerances and the quality of its manufacture are also not insignificant. On the other hand, using a robot and screwing from a learned point while adjusting a whole range of movement parameters does not always pass the test.
Situation found
The customer is a manufacturer of equipment for the construction and finishing industries. The products are shipped to European markets. Ensuring quality and repeatability of production is crucial.
When automating the screwing of a nipple (male thread) into a profile (female thread), many jams occurred, leading to high material rejection and production delays.
The problem
The thread was out of tolerance, and its shape and outline deviated from the nominal. It was cost-prohibitive to interfere with the forming process, and a very big problem was the "false" thread outline located exactly in the middle of the pitch of the actual thread. Its pitch was equal to the proper thread, but the depth was only 1/4 .
Such parameters of the "false" thread allowed for the initial screwing of the nipple, but due to the smaller depth it caused jamming during screwing. "False" thread started about 20-30 degrees before the right one.
The jamming turned out to be so strong that there was no way to automatically correct the process. Even slowing down the speed of axis 4 (rotation) and reducing the torque caused the workpiece to jam. Adjusting the feed rate during screwing had no effect.
There was a need for more repeatable screwing to reduce the number of variable factors and be able to adjust the process.
Solution
The solution concept was to detect the beginning of the actual thread, that is, to screw in at the same angle of the nipple thread relative to the beam thread. But how to find the reference point?
During the movement in the direction of unscrewing, the thread slides in the bore of the beam. It can be seen that it rises slightly during the rotational movement, then falls sharply into the hole - indicating the beginning of the thread coil. However, the amplitude of the vertical movement is small. Nevertheless, it is possible to consider this moment as a reference point for setting the angle when starting to screw. It was necessary to select the appropriate fixture, based on the distance measurement.
How does it work?
Given that the machine had already been put into service for the customer and the need to stop production, larger upgrades were out of the question. Therefore, we were looking for a sensor that would minimize the amount of installation work.
The choice fell on BOS0285- analog optical rangefinder with interface IO-Link.
The machine already had network islands installed Balluff BNI0077equipped with the IO-Link protocol. Their use reduced the current installation to only running a single cable to the sensor.
A puck was mounted in the axis of the screwed-in nipple, on which the sensor beam falls. The puck changes height according to the position of the nipple, which is registered by the sensor. This process can be seen in the graphs below.
The signal was significantly "noisy" due to the high roughness of the threads. However, proper filtering and analysis of the signal in the PLC enabled precise detection of the characteristic point.
Customer benefits
The introduction of repeatability in the screwing process has translated into a reduction in the number of jams during nipple assembly. This increased production volume and reduced overloading of the robot's axes, resulting in a longer service life.
Greater control over the screwing process also enabled individual parameterization for each reference, maximizing process reliability.
About the company
Machine Design has been involved in automating manufacturing processes for 27 years. The main industries are automotive, household appliances, and other specialized industries. We implement projects throughout the country and abroad. Our experience and infrastructure allow us to build large automated production lines, reaching up to about 100 assembly and testing stations.
The scope of our realizations includes, among others:
automatic test stations using the latest measurement technologies,
semi-automatic assembly stations.
We treat each realization in a unique way. We customize solutions to optimize the functionality of machines and maximize their efficiency. Each project is a joint venture between us and our client. Together we define the project assumptions, then develop the design and build the machine. We not only deliver the finished equipment, but also assist during its commissioning, as well as train operators, process and maintenance engineers.
The published case study participated in the Balluff Case Study Challenge 2023, which aimed to published case study participated in the Balluff Case Study Challenge 2023, which aimed to recognize and reward the most innovative case studies submitted by industrial machinery manufacturers.valuing and rewarding the most innovative case studies submitted by mOpublished case study participated in the Balluff Case Study Challenge 2023, which aimed to recognize and reward the most innovative case studies submitted by industrial machinery manufacturers.industrial machinery manufacturers.
The published case study participated in the Balluff Case Study Challenge 2023, which aimed to appreciate and reward the most innovative case studies submitted by industrial machinery manufacturers.
Keywords
- Case Study
- IO-Link
- Industrial automation
- Efficient production
Author

Balluff Sp. z o.o.
We have been active on the Polish market for more than 25 years. We serve our customers from Pomerania to the Tatra Mountains, providing first-class service and technical support. We are also present online, where we share our knowledge about the latest implementations, industry trends, events or technical aspects of our solutions.
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