This article is a summary of Dr Mario Walther's doctoral thesis (see sources below in German).

What is the best way to measure force in production, and why is it important? 

Assembly forces applied in production can represent risk factors for the development of health disorders. This risk increases considerably with age, and can therefore increase absenteeism due to illness. Moreover, companies that fail to implement ergonomic measures also have to pay the high costs.

So it's important to put people and their health first, by recognizing and eliminating risk factors at an early stage!

In order to measure these assembly forces in a practical, human-influenced way, and to carry out effective measurements, the intervention of ergonomists in the workplace with force-measuring instruments is recommended. These measurements provide objective, detailed and accurate results of the human body's stress variables. For this, ergonomists need the most accurate measuring instruments available.

High forces exerted by hand

It is in production, and more specifically in the assembly area, that the greatest number of actions involving manual force are performed. The assembly of quick-fit fittings, connectors and linings is associated with repetitive, high hand and finger forces, and represents a fairly high risk for installers. High assembly forces, poor posture and insufficient rest periods can damage health. Assembly dimensions and materials also play a decisive role in the application of force.

Early consideration of ergonomic aspects can lead to improvement measures that can reduce or prevent risk factors. For example, companies can significantly reduce the assembly forces required by developing easy-to-assemble components at the design stage, and workstations and tools can be designed more ergonomically.

To take account of these ergonomic elements, practical measurements are needed which, above all, define the actual assembly force.

Why does joining force not correspond to impact force?

It's important to distinguish between assembly force and impact force. Assembly force is the force required to assemble a component. The force exerted by the assembler after insertion is the impact or holding force. Because of the short time available to an assembler for this task, it is often impossible for him to reduce his efforts sufficiently. When the force exerted is close to the force to be exerted, the job is done efficiently. Otherwise, the effort can lead to illness.

When using a force gauge for ergonomic measurement, which only measures the maximum, it is not the assembly force but the impact force that is determined. Assembly forces involve high-frequency vibrations of the order of 250 Hz: too low a measurement frequency means that the difference between assembly force and impact force cannot be determined, due to the rapid assembly method. This leads to a lack of feedback on the assembly process and may result in the application of a higher force.

The solution: the Centor Touch force gauge

Andilog's Centor Touch force gauge is a flexible and sophisticated solution for practical measurements in production areas. This cost-effective, robust and highly accurate force gauge is equipped with strain gages and enables rapid measurements without disrupting work processes.

The Centor Touch measures at a sampling frequency of 5000 Hz, enabling even the smallest force fluctuations to be measured. It offers automatic calculations such as the first break (joining force) and the maximum of the complete test (impact force or holding force). The curve is displayed on the screen in real time, enabling the fitter to judge whether it has been carried out correctly immediately after measurement. Adjustable force thresholds in Centor Touch allow the user to enter the force to be exerted: an acoustic signal tells the fitter when the desired value has been reached, and he can stop the measurement.

As the direction of the force influences the measurement, Andilog has developed small pressure plates (Ø20 and 8 mm), which help the tester to measure the ideal joint axis. The values determined are highly precise, and the calibration certificate supplied guarantees accuracy of 0.1% over the sensor's entire measurement range.

Centor Touch measurement results

Centor Touch offers excellent value for money, with realistic test speeds. Measurement starts manually after a predefined force has been applied, and ends automatically after a set period of time.

 

The touchscreen displays the two forces calculated at 5000 Hz that every ergonomist wants to analyze: the assembly and impact forces. The curve determined can be compared with the target curve, and if correct, the curve points can be saved on a USB stick.

 

In Datastick II, the 4 phases of assembly - force increase, assembly force, support and force decrease - can be marked and exported to reports. Ergonomics managers can thus increase the acceptance of ergonomic measures within the company thanks to precise, objective results.

Conclusion

Concrete ergonomic measures can only be implemented on the basis of concrete measurement results. But they also require the awareness and goodwill of the employees and managers concerned. In this way, employees can optimize the force they apply so that it is as low as possible but as high as necessary. Departments involved in product development can design the properties and materials of their components in such a way that high assembly forces are reduced or even prevented. As a partner in ergonomics, Andilog offers a compromise between high-precision measurement and flexible use directly on the assembly line.

Ergonomics is the result of collaboration between all departments and partners within a company. It plays an essential role in the process of making people the company's main resource, and restoring their health and value-creating potential. Andilog also sees itself as a player and partner in this field.

 

Source: Mario Walther, 2015, "Développement et évaluation d'une procédure systématique d'enregistrement des forces de montage dans la production automobile", Entwicklung und Evaluierung eines systematischen Vorgehens zur Erfassung von Aktionskräften in der Automobilproduktion, genehmigte Dissertation zur Erlangung des akademischen Grades Doktor-Ingenieur, Fakultät für Maschinenbau der Technischen Universität Chemnitz

Document available on the qucosa website.