Seeing is believing
A vision system helps quality control in tablet packaging

A pharmaceutical manufacturer in south Germany uses a vision sensor for quality control in the filling of tablet tubes to check that the sealing plug and retaining ring are present and seated properly. Faulty tubes are automatically discharged. The system learns from experience, can easily be adapted to different products, and integrates seamlessly into existing automation frameworks.

The vision system at the Wolfratshausen plant of Hermes Arzneimittel (Pharmaceutical) was installed because the previous seal checking system, based on a simple photoelectric sensor, was not very accurate. The reflex-type photoelectric sensor was able to detect the presence of the sealing plug, but could not check its position or that of the retaining ring. This resulted in a good deal of rework, especially since faulty tubes needed to be unpacked and repacked before they could be properly sealed.

To improve matters, Hermes equipped one of its filling systems with a Simatic VS 110 vision sensor from Siemens. The complete package, consisting of a sensor head (camera), infrared illumination system and processing unit, was designed to detect unsealed or improperly sealed tubes under all conditions and ensure that faulty ones are removed straight away.
Hermes Arzneimittel, founded in 1907, has been producing effervescent vitamin tablets since 1994. The company now manufactures these at the rate of more than 750 million per year, packaged in sealed tubes or strips. Hermes Arzneimittel sells its own over-the-counter products under the brand names Optovit, Biolectra, Calcimed, Ajuta and Optolind. It also develops and manufactures drugs for global pharmaceutical companies at Wolfratshausen and another plant in Austria.
Strong growth in vitamin tablets led the company to move from Großhesselohe, south of Munich, to Wolfratshausen in the Bavarian uplands. Production at Wolfrats- hausen is carried out on 13 fully-automatic production lines on three levels. About 200 employees working in two shifts process approximately 15 tons of raw materials into semi-finished and finished goods.
The packaging line on which the vision system was installed handles two tube diameters (26.5 mm and 29 mm), in lengths from 75 mm to 175 mm. The new checking system therefore required a high degree of flexibility, with quick changeovers to mini- mize unproductive downtime.
Looking for the perfect system
Another stipulation by the operator was that the vision sensor had to be integrated into the existing control system. This would allow the existing multi-panel Simatic MP 370 Touch unit, for example, to be used for setting up and training the vision system to handle new products. This was not a problem, given that Hermes already used Simatic components almost exclusively in its control systems.
The vision system was required to check not only for the presence of the sealing plug, but also that both the plug and the seal retaining ring are properly positioned. The filling line’s belt speed of 5 – 15 m/min corresponds to a maximum of around two tubes per second. The Simatic vision sensor can acquire up to 25 elements per second, so it has ample reserves for higher throughputs.
Hermes technicians installed the vision system at right angles to the upwardly-inclined conveyor belt. On one side of the belt is the camera, and on the other is the infrared illuminator. As each tube passes the camera, a trigger signal causes the illuminator to produce a flash of infrared light. The camera records the silhouette of the sealing plug and retaining ring, regardless of the ambient lighting. The information passes to the processor unit, which compares the silhouette with a stored template and decides whether to accept or reject the tube.
The system uses an adjustable parameter known as the Y limit to accommodate positional errors arising from sources such as vibration of the conveyor. To handle allowable differences in the positioning of the sealing components, the user can define a variance template based on two outlines, known respectively as OK_A and OK_B. If the permissible deviation—the Q limit— is exceeded, the system identifies this as a missing or misaligned sealing plug or retaining ring and switches a corresponding digital output. This signal can be transmitted to a PLC or directly to a valve cluster, enabling autonomous solutions to be created without the need for additional controllers.
The sensor head uses a CCD chip to capture images at a resolution of 640 x 480 pixels. It has a fixed lens, and only needs to be plugged into the analyzer and the infrared illuminator. The whole system is rugged, for operation at vibration levels of up to 1 g, shocks of up to 70 g and temperatures of 0 – 50 °C. The sensor head is sealed to IP 65 and the illumination unit to IP 40.
Training and growing
The VS 110 analyzer can store up to 15 different reference images, allowing the unit to be used with a corresponding number of different products. Reference images are retained in the event of a power failure. The appropriate reference image and associated parameters are chosen from either at the analyzer itself or, as it is done at Hermes, through the multi-panel Sima- tic MP 370 Touch, the Profibus DP fieldbus and the high-level Simatic PLC that controls the filling line.
New profiles can be added to the VS 110 system either directly or through a PC connected to the unit. In the case of the Hermes plant the PC is a touch-screen unit running Windows CE, giving a simple system that was quickly mastered by the machine operators. Possible errors during the training run can be remotely acknowledged, which saves long walks to the control cabinet containing the analyzer. “Siemens helped us with support during the commissioning process,” adds Helmut Jakolat, the site’s production engineering manager.
“Our first production line equipped with the vision system has been operating absolutely reliably and trouble-free since July 2004,” says Jakolat. “From that time on, the number of faulty tubes reaching subsequent process stages has fallen practically to zero, and we can guarantee that we are only delivering perfectly sealed products to our customers.” In the future, the company plans to extend the use of Simatic VS 110 vision sensors to the other lines on the plant.