At the end of November 2019, STÖBER Antriebstechnik presented the new generation of its servo planetary geared motors for the first time at SPS IPC Drive in Nuremberg. These drives are the most compact on the market in their power range and with their exceptional diversity of combinations and options. To also ensure consistently high quality for this series in final assembly, the specialist developed another end-of-line test bench specifically for the new generation at its headquarters Pforzheim. This ensures that STOBER only offers its customers tested and documented planetary gear units and motors.
The new generation of servo planetary geared motors from STOBER allows customers to build even more compact systems and increase performance at the same time. Thanks to the exceptional variety, engineers have all the options in the design phase to put together exactly the right drive solution for any application. "Of course, we only want to offer our users solutions that meet our own standards for quality," says Michael Fitzer, Central Planning Technology at STÖBER Antriebstechnik. And these are high standards. "That is why we have now developed a special test bench for the final assembly of the new generation, as we have for nearly all of our series, which is set up at the end of the new production line." As a result, every drive that leaves the factory is tested and documented.
Fitzer points to the monitor. "We test various aspects of the planetary geared motors, such as the output speed, gear ratio or radial runout." The test bench calculates the gear ratio automatically using a constant input speed that is compared with the output speed. This allows the technicians to immediately recognize if the gear sets are installed incorrectly. And this is just one example.
The concentricity test, for example, is particularly used for attaching gears to the output. For this purpose, each tooth flank is scanned at the test bench, which is used to determine the concentricity. "If we want, we can also represent this graphically on the screen," says Fitzer. If deviations emerge, an employee can adjust and secure the output gear right at the test bench using special tools. This way, STOBER meets customer requirements and can guarantee concentricities in the minutest micrometer range.
Testing the total friction coefficient plays an important role, according to Fitzer. This test makes it possible to draw conclusions about the quality of the assembly work, such as about the preload forces of the bearings. Using a corresponding soundproof cowl and special software, the employee can locate minimal noises using a headset at the test bench. These can be caused by the slightest damage to the tooth flank, for example. At the same time, the employee can also check the running noise of the gear unit.
The Test Bench—Developed intelligently
"In the development of the test bench, which we named EoL 4.XX, we placed great importance on ergonomic operation," describes Fitzer. As a result, employees can work at a comfortable height. The gear unit or geared motor is clamped and removed automatically. As needed, the employee can handle parts comfortably using a crane, for example, set them on the test bench and remove them again the same way. The soundproof cowl is also opened and closed fully automatically.
"We developed special software with which we can optimize the test cycle for each gear unit," explains Fitzer. Simply put, the program regulates the input speed for gear units with a high gear ratio, and thus runs at a corresponding output test speed. This shortens the lead time.
There is also the issue of safety, which already takes top priority at STOBER. "Even before the construction and design of our new test bench, we brought in trained safety specialists as consultants," says Fitzer. As a result, the EoL 4.XX is equipped with a side access guard and with a safety curtain on the front. The safety curtain is able to stop the testing process or movements of the soundproof cowl immediately in an emergency.
The new servo planetary geared motors are available in different sizes. The test bench is flexible and can be used for all types of the series up to sizes P8 and PH8. "We can operate and test all our synchronous servo motors with wide-ranging encoder variants," says Fitzer. "Even coupling variants make no difference."
The operator can monitor the test process using a webcam at all times, even with the cowl shut. The test results are continuously checked by plausibility monitoring. "The test cycle starts first by the system scanning the barcode," says the STOBER specialist. This loads all the set data from an internal database, which is then compared with the actual data during and after the test process. The screen displays the results. If everything matches, the values are green; if they fall too low or too high, they are highlighted in red. "Using this database, the EoL 4.XX also checks previously completed assembly work automatically," explains Fitzer. For example, the operator sees whether the tightness test has already been carried out, or if the gear unit was filled with oil. "Since the beginning of the year, we have been working fully digitally in picking components and in assembly," says Fitzer. "This means that after the system has scanned the barcode, the employee only sees the corresponding work instruction on the monitor at their workstation. When the order is completed, the test bench reports this back to the SAP system." STOBER also relies on digital tools in assembly planning, such as a digital twin of the assembly environment and testing using VR goggles.
This new development from STÖBER Antriebstechnik enables a standardized process for quality assurance for the new servo planetary gear units and motors, which will also be applied in all other assembly plants. As a result, the satisfaction of customers is always ensured.