UKM-SUM23-PG38+39_Layout 1 27/04/2023 11:20 Page 39
GEARS & GEARBOXES
B10 life, the time at which devices have a 90 per cent probability or more of survival. Throughout the pre-defined timescale of the test, observations are made at regular, defined intervals from which data analysis can take place. The typical goal is zero-failures at the testing conclusion. If failures are observed before this time is reached, the required test time will be recalculated. If a low number of samples fail during testing, the failure data can be analysed with the Weibull Method, a life data analysis that determines trends of a relatively small data sample, to calculate the achieved reliability.
TESTING IN PRACTICE
As a real-world example of RDT testing, Portescap designed a DC gearmotor for an infusion system developed by a medical device manufacturer. To validate reliability, the specification required an operational life of 10,000 hours, tested to achieve 95 per cent confidence. This required a B10 life calculation with RDT performed under an accelerated model. As a gearmotor’s operational life is primarily dependent on the applied load and application conditions, the engineering team selected torque and speed as the stresses for accelerating the test time. The inverse power law, commonly used to test non-thermal accelerated stresses, would be used to calculate the acceleration factor. As the specified torque requirement for the actual application was 10 mNm, for the acceleration factor calculation, the torque for the accelerated stress was set at 25 mNm, with a constant speed of 200 rpm. Then, the test duration was set using a parametric binomial method, preferred when the real lifetime of the device will exceed the allowed test duration. This generated a test time of 1,081 hours considering zero failure cases. Using Weibull calculations, a sample size of 10 gearmotors was set. To perform the RDT, the required torque level was applied to the gearmotors, maintained using a hysteresis brake, acting as a torque limiter. Performance parameters were recorded daily, including voltage, current, speed, and temperature. On conclusion of 1,081 hours, all gearmotors completed the test without failure or abnormalities, and the required B10 life of 10,000 hours with 95 per cent confidence level or more was validated.
SYSTEMATIC APPROACH CONFIRMS RELIABILITY
A systematic approach to RDT achieves significant confidence in the operational lifetime of DC gearmotors. Even when actual life test duration is not a practical possibility, a robust RDT procedure creates high reliability in accelerated life testing. Portescap’s engineers work alongside OEM teams to design and implement RDT whenever a project requires it. Systematic RDT does not just assure confidence but creates actual reliability for real-world use.
Portescap
www.portescap.com
UKManufacturing Summer 2023
DRIVE TECHNOLOGY FOR ROBOTICS
Drive technology that meets the requirements for robots and AMRs is very popular. The Bonfiglioli Group, which operates worldwide, has a wealth of know-how, experience and comprehensive manufacturing options for customer and machine-specific solutions, serving the industry with competitive gearboxes and gearmotors. The diverse product examples supplied to robotics by Bonfiglioli range from individual components such as shafts and gear wheels, complete low-backlash gearboxes for axes 1-3 of buckling arm robots to compact electromechanical drive solutions for AMRs.
workpiece, power. The base, the carousel as the first axis, rotates the entire robot around its own axis, the so-called swing arm is tilted by a second axis and the third axis tilts the arm. Bonfiglioli serves these three axes with robot-specific solutions, i.e. gear units specially designed for each robot series and size, which are developed and implemented in close cooperation with the customer. The best example of this is the cooperation with ABB Robotics. In addition, many other components for transmitting torque, i.e. shafts and gears, are also supplied, which are developed to meet the requirements of the specific application as well.
R
obotic motion is all about speed and accuracy, and
depending on the size or weight of the tool or
For driving autonomous mobile robots (AMRs) and AGVs, a sophisticated modular system consisting of gearboxes or geared motors including a drive wheel is available, which can be perfectly tailored to all customer needs. The platform called BlueRoll, the heart of which is the TQW wheel drive series, consists of three versions: In the basic version, the customer is completely free in terms of the motor. With the advanced or with the compact versions, Bonfiglioli also supplies the motor fully assembled and ready for installation. In-house brushless AC motors with voltages starting from 12 volts including the cabling are available for this purpose. A single unit of the three available sizes of BlueRoll devices can be loaded with up to 360, 720 or 1,020kg and reaches speeds of up to 2m per second. In addition, Bonfiglioli always has the option of adapting the system components to very specific customer requirements.
The Bonfiglioli Group
www.bonfiglioli.com
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