FEATURE Sensors & Sensing Systems
Factors for measuring thickness in battery production
What are the challenges in making reliable battery- thickness measurements, asks Glenn Wedgbrow, Business Development Manager at Micro-Epsilon UK
T
he growing demand for energy-storage devices such as lithium-ion batteries and fuel cells are being met by
Giga factories that are equipped with effi cient, highly-automated production lines. To optimise battery production, sensors are required that monitor the production line to the highest accuracy and dynamics. These sensors include high-precision distance sensors, infrared temperature measurement technology, as well as 2D/3D-profi le sensors for various measurement tasks involved in battery production such as electrode manufacturing, assembly and forming processes.
In battery production, one of the key quality-control parameters is the thickness (and width) of fi lm and strip materials, wet layers and electrode coatings. These require sensors that measure it reliably as the material is being processed (inline), optimising production yields whilst minimising waste. All manufacturers will have a process specifi cation to meet in order to satisfy their customers. But, in reality, how can a manufacturer be sure they are meeting these specifi cations at all times, and to what challenges? Several diff erent measurement systems can measure the thickness of a material. Some of these are used offl ine, i.e., random samples of the material are removed from production and measured to verify that they meet the specifi cation. A more eff ective approach is to install an in-process or fi xed, inline, non-contact measurement system that continuously measures the thickness of the material as it is processed. If measurements from these systems move towards the outer limits of the specifi cation, machine and process control parameters can be altered to bring the thickness back into acceptable limits.
18 November 2021 | Automation
While many suppliers state on their datasheet that the measurement system meets a certain resolution and linearity, in the real world this performance is aff ected by a number of environmental infl uences. Errors associated with real-world thickness measurement are not always so obvious, but can combine to create signifi cantly large errors. It is therefore critical to select a system based on system accuracy, not just sensor accuracy.
Alignment and target movement Special attention must be paid to the alignment of the sensors, which are typically installed opposite one another. No misalignment, tilting or inclination of the sensors relative to the target object is permissible in order to ensure the sensor spots are measuring at the same point all the way through the measurement range. For example, for a misalignment of 1mm and an inclination of 2° there will be a thickness measurement error of 35µm. In the case of a 10mm target thickness, this error increases to 41µm. Combined linearity errors of up to 8µm, for example, can be seen with a vertical target movement of just 200µm of the target in the measurement fi eld even if the target has the same thickness. As a supplier of non-contact inline thickness measurement systems, Micro- Epsilon has developed its own methods of precise sensor alignment and patented algorithms for this process. To avoid thickness calculation error due to movement of the target, both sensors must be perfectly synchronised so that they perform the measurement at the
same time, at the exact opposite point of the target. If synchronisation does not occur, inaccurate measurement data is produced. For example, if measurements are taken at diff erent time intervals, micro-vibrations of the target or of the sensor mechanics will result in a thickness measurement error.
Sensor accuracy/linearity Each measurement sensor has its own measurement uncertainty, often referred to as ‘linearity’. This means that at any given point in the measuring range, the actual reading from a sensor can vary by a percentage of its measuring range. The challenge is that no sensor is the same, so errors caused by non-linearity can add or subtract in the fi nal result. Micro- Epsilon has overcome this challenge by performing a combined, patented calibration of both sensors to create a new, signifi cantly-improved thickness measurement linearity. It is also extremely important to design a mechanically- and thermally-stable sensor-mounting frame that is isolated from process or machine vibration. Thermal expansion of mounting materials can be a source of large errors in thickness measurement, so choose materials with low thermal expansion coeffi cient. Micro-Epsilon off ers integrated automatic thermal compensation to eliminate measurement errors.
CONTACT:
Micro-Epsilon
www.micro-epsilon.co.uk
automationmagazine.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48
