Designers of robotics and automation solutions are often faced with a choice: cycloid or planetary gears? In the last few decades, the answer has often been cycloidal drives. But the planetary gears have caught up and are now superior in many ways. The Hamelin company Schaeffler Ultra Precision Drives (previously Melior Motion) has revolutionized the planetary gear and with its PSC series, produces extremely precise, quiet and durable drive units.


Compared to cycloid drives, gears from Schaeffler Ultra Precision Drives are a lot more precise. In concrete terms, this means: You have a torsional backlash of ≤ 0.1 angular minute and a lost motion of ≤ 0.6 angular minute. Most cycloid gears can only come up with a torsional backlash of ≤ 1 angular minute – the PSC gears are up to ten times more precise. This very high accuracy has its origin in the conical toothing of the second stage. This presses the teeth of the planetary gears into one another and ensures that the transmission is free of backlash.

Constant low backlash

There is one main reason why the drive solutions in the PSC series are so much more precise than normal planetary gears and cycloid gears, not just for a short time, but over their entire service life: a component the size of a fingernail. More precisely, a self-regulating gear system. The overall system is patented and ensures lifelong freedom from backlash. It compensates for the wear and tear of the tooth flanks and avoids time-consuming readjustment and the associated downtime of the machines. Even after a long period of use, the gearbox remains as precise as it was at the beginning and thus clearly stands out from other (cycloid) gearboxes.

Precision is the figurehead of every robot and many automation applications, so it is a significant benefit, when the robot/system is still working just as precisely after several thousand hours of operation as it was at the beginning. In contrast to other drive units, the PSC gearboxes allow 20,000 or, depending on the application, more operating hours without loss of precision. An efficiency of more than 90 percent, significantly better than cycloid systems and an extremely low breakaway torque ensure outstanding energy efficiency. As a result, the gearbox temperature remains at a consistently low level, meaning that wear parts and lubricants have a longer service life.

Quiet and low-vibration thanks to the helically toothed input stage

In some industries, such as medical technology, it is not just about precision, but also about low noise. In the treatment or operating room, noises are perceived very differently than in a huge production hall. A quiet environment is important for the patient's well-being. And when it comes to occupational safety, quiet gears have an advantage in all industries. The PSC gear makes the helically toothed input stage particularly quiet in operation. Significantly quieter than other planetary or cycloid solutions are. With a running noise of less than 65 dB (A), this makes a clear difference, especially in applications with multiple gears.

The low level of vibration goes hand in hand with the low noise. On the one hand, this is due to the very precise involute toothing that all planetary gears have in common. It enables a highly efficient rolling movement. Cycloid systems based on a sliding movement with offset rotating cams cause more vibrations and wear. On the other hand, the low vibration is also due to the helically toothed input stage, the specialty of the PSC gearbox: At high speeds, a smooth and even run is given. Again, this is not only relevant in the medical field, but also, for example, for rotary tables on machine tools.

Can be flexibly adapted to the application

A low breakaway torque means good controllability for the user. Especially during the start-up phase and at low speeds. Due to their design, planetary gears generally have an advantage over cycloid gears in this regard. The PSC systems even have an additional element which further reduces the breakaway torque. In front of the planetary gear there is a gear stage, consisting of just a single pinion and a gear. Both are helically interlocked. Since only a few components are moved in the first step, a large ratio of up to 16:1 is created in the first stage. In the case of gearboxes with a low breakaway torque, the drive motor and control system can be designed to be smaller, incurring lower cost and power consumption.

Compared to other drive units, the PSC drives have another special feature that can mean a great advantage for the user: the motor has moved out of the middle. What is already necessary for hollow shaft gears, Schaeffler Ultra Precision Drives also uses for its solid shaft gears. The changed structure allows much more flexible planning. Designers can – if desired – build the system or the robot around the gearbox. The expanded options come into play especially when engineers include the PSC gearbox in their planning as early as possible.

With its PSC gears, Schaeffler Ultra Precision Drives does away with old prejudices and proves how much potential there is in planetary gear technology. Due to the special technical features, the drive solutions put cycloid gears in the shade in terms of precision, durability and background noise. PSC precision gears are therefore a real alternative for application scenarios in which planetary solutions have previously played a subordinate role.

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