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Tracing sources of error in plant operation

16 August 2016

Time and money is being lost at production plants due to problems not being fixed in a timely fashion. Faults can often be identified, rectified, and prevented from recurring by tracing mechanical errors with specialised high-speed recording cameras.

There are huge commercial pressures today for production systems to run at their full potential at all times and to provide consistently high quality without interruptions, shutdowns or wastage, in practice however this is rarely achieved and the best-laid plans to meet productivity targets are often thwarted by real-world realities. Products and employees change, tools and equipment wear out, and lines have to be slowed because of unanticipated wastage at target speed.  All these factors can mean that the return on investment in production plant remains below expectations. 

Worse still, the causes of production line problems can be difficult or impossible to identify. Mechanical errors in production equipment can happen when workers are temporarily away from the line or, more commonly, occur so quickly that they are impossible for staff to detect until it’s too late. When producing at a cycle rate of, say, 100 pieces per minute, every second counts - but the human eye and brain simply cannot work at these speeds.  

However, these disruptive and expensive puzzles can often be solved more easily than many plant operators realise. The answer lies in the use of specialised high-speed recording cameras. Unlike image processing cameras, which plants use as quality assurance to prevent the delivery of faulty parts, high-speed cameras make production processes visible, allowing plant operators to document specific parts of the production process. Detailed frame-by-frame analysis of photographic images can identify the cause of a problem. This usually leads to the plant being brought up to planned productivity – and in some cases the documentation process makes it possible to boost productivity even further. 

High-speed recording cameras are being used successfully in many industries today, filing systems for beverage production, presses for sheet metal processing, packaging machinery for food production, pharmaceutical labelling systems and robots in the automotive industry   
Frame-by-frame fault capturing 
Production plants can be vast and are often divided into many different lines and processes such as moulding, pressing, packaging, assembling, testing, labelling, crunching, and pick-and-place. A high-speed recording camera can usually be installed at all of these processes and is typically relocated from one station to the next, wherever the production line is not working as it should. Cameras designed for use in difficult conditions, such as poor lighting, temperature fluctuations, and vibrations are available and some can even go into very cramped spaces. 

The camera’s field of view is determined by selection of the appropriate lens. Modern sensors make it possible to find the right combination of resolution, high frame rates, and sensitivity. The MotionBLITZ Cube4 camera from Mikrotron, for example, can take up to 1,000 images per second at a resolution of 1280 x 1024 pixels, and with a smaller region of interest the frame rate can be increased to as many as 93,000 frames per second.  The recorded video can be played more slowly by a factor of 20 to more than 1,000 and, with the help of Windows-based software, visually analysed frame-by-frame. 

High-speed recording cameras use a ring storage device which, when completely filled, is overwritten. When an error occurs on the production line, the camera is sent a signal – by a person watching the process, by a sensor connected to the camera, or when the camera detects a change in brightness in the image – and recording is stopped. The video material recorded up to that point remains on the internal memory and can be downloaded for analysis via an Ethernet port. Alternatively, there are cameras with an integrated large screen where videos can be viewed via a touch screen interface, edited, converted, and transferred to an SD card. This enables work on location without the need for a computer.
Reducing errors 
A good example which shows the value of high-speed recording cameras can be found at Varta Consumer Batteries. The company’s plant in Dischingen, in Germany, specialises in dry batteries –from single-cell to micro-cell (type AAA). Every step of the manufacturing process is undertaken at the plant – assembly, fitting, filling, labelling and packaging. Every day approximately three million cells move through the rotary transfer systems, conveyor lines, test equipment and packaging machines to their final destination in the dispatch bay. 

Varta’s newest-generation batteries perform particularly well as a result of a specially formulated electrolyte which is injected into the battery casing. This filling process requires precise dosing when only a few hundredths of a second are available. Varta had initially encountered problems with a missing electrolyte drop changing the battery characteristics and contaminating the production line. This was causing product rejections because of unacceptable fluctuations in the individual batteries’ performance, and was forcing expensive maintenance downtime on the production line.

High-speed recording cameras offered a solution. After conducting slow-motion studies, process parameters were quickly adjusted so that the quality requirements could be met while maintaining a very short cycle time.  Josef Graule, project engineer at the plant explains: “After making only a few high-speed recordings, we were able to select the filling jets in such a way that the filling process ran without any more troublesome splashes. 

“Next, the camera provided us with information we could use to constantly reduce bottlenecks in the production flow.” Within the first year, investigations of more than 20 points in the production process led to a substantial number of optimisations. 

A camera also enabled clear improvements to be made in the battery labelling process. Fitting the cells with wrap-around labels has to be done with a high degree of precision at speeds of 900 to 1,000 parts per minute. Improperly labelled batteries result in rejects and material loss, with any consequent jams in the labelling process causing downtime. As it was necessary to record this process from the side, the contour of the label was visible only as a very thin line, but the high image resolution of the camera made analysis possible. 

Prevention is better than cure 
Using cameras also enabled Varta to set up a continuous measurement inspection point. For the first time, a new laser measuring system for quality control could be precisely mounted because slow-motion video revealed the exact point on the batteries at which the measurement was to be made and at which point the measurement could be obtained with the system turning at full capacity. The camera’s integrated time-stamp function, which is applied to each individual frame, enabled processes to be calibrated to the millisecond. 

“The additional integration of control signals in the high-speed recording process provides even more valuable information for the optimisation of the process, as multiple steps must often be coordinated with each other on single machines. I am sure that we will implement even more prevention in the future,” concluded Graule.

The progress made at the Varta battery factory is just one of many examples of high-speed recording cameras tracing troublesome glitches on production lines, providing the detailed information that leads to a solution, then helping to identify and prevent potential disruptions before they occur. 
Max Scholz is product manager at Mikrotron GmbH

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