Automated handling of uneven stacks at Fresenius Medical Care SMAD
Fresenius Medical Care SMAD uses a smart system to handle uneven stacks of dialysers. This system consists of a robot that uses two 2D sensors to detect the position of dialysers and move them to a conveyor without any human intervention 24 hours a day, 7 days a week.
Fresenius Medical Care SMAD is a global leader in kidney disease treatment, offering a comprehensive range of services and products for patients with chronic kidney failure.
The dialyser production line at its plant at L'Arbresle, in east-central France, is equipped with a robot. "In 2009 we decided to automate our dialyser handling unit, which is located between a conveyor system and a processing unit. Automating the unit was an obvious solution. The main challenge was that the dialysers are stacked unevenly and their positions vary along three dimensions. We had to find a system that could recognise their positions," says Mouloud Ifri of Fresenius Medical Care SMAD's Manufacturing Department.
Automating the line was particularly necessary for two reasons: it is installed in a controlled environment – problematic for human intervention – and it operated at high speed 24 hours a day, 7 days a week.
The feed system consists of two conveyors, each with two rows of dialysers. The robot is equipped with a tool that allows it to pick up two dialysers per cycle. The tool is fitted with two Keyence LJ-G080 laser sensors, one per dialyser, so that the dialysers are correctly picked up one after the other.
The robot thus simultaneously removes dialysers from each stack on a conveyor. It takes dialysers from the two conveyors in turn. When a row (diagonal) is emptied, the conveyor moves forward until the stack reaches the unloading position.
The robot routinely 'scans' the theoretical positions depending on the type of product. It uses the Keyence sensors to detect products and correct its pickup position accordingly. If no products are detected, the robot moves to a different stack. It also uses the sensors to correct its X- and Z-axes. To compensate for dispersion along the robot's Y-axis, the robot's tool is fitted with a homing cylinder for each type of dialyser. The maximum height and slope of the stacks are always the same for the same type of product. However, these stacks may be uneven.
"We first considered installing an industrial vision system. However, the cost and complexity involved led us to scrap that idea. We then looked at a 2D laser measurement sensor provided by a competitor, but found it to be complicated to implement."
Ultimately, Fresenius Medical Care SMAD chose the LJ-G080 sensor by Keyence. Its user-friendly setting menu means that experienced and novice users can configure settings easily and quickly. The setting support software (LJ-H1W) supplied with the device makes it easy to save and analyse data with a PC. Configuration is also made easy by several adjustment functions.
The position adjustment function provides stable measurements even when targets are not perfectly arranged or positioned.
The tilt correction function simplifies installation of the sensor head and eliminates measurement errors.
A number of functions make measurements the surface properties of targets (shiny, dull, etc.).
"We also place very high demands on the robustness and reliability of equipment," adds Mr Ifri. {The LJ-G sensor delivers reliable detection over time, offering repeatability of 1 micron along the Z-axis and 10 microns along the X-axis. Particularly robust, it is protected inside an IP67 housing and withstands vibrations (tested from 10 to 55 Hz, with an amplitude of 1.5 mm, for two hours along X, Y and Z). It weighs 350 g and has a detection range of 80 mm. {
Fresenius Medical Care is present worldwide and employees 65,000 people. It is a subsidiary of Fresenius, a healthcare company with 125,000 employees.
Fresenius Medical Care SMAD has 450 employees. Its operations are primarily focused on the production of two main types of product:
- dialysis filters (aka dialysers),
- bags of dry or liquid concentrates. Concentrates are salts that are used to prepare dialysis fluid, which is similar in composition to blood plasma.
