HISTORY AND BENEFITS OF BALL SCREWS AND PLANETARY ROLLER SCREWS

History and Benefits of Ball Screws

Ball screws were first devised as a linear motion feeding mechanism for press machines. Such screws can be found in a U.S. patent filed in 1874, shown in Figure 5, as well as in a German patent filed in 1879. Also, a British patent filed in 1909, shows a mechanism with almost the same structure as ball screws in use today. The first practical use of ball screws is thought to have been in airplanes during World War II (1939- 1945).

Figure 5: U.S. patent for ball screw mechanism (1874)

Figure 6: A recent example of application to an automobile's steering gear

The first mass-produced products are said to be those applied to the front wheel steering mechanism in automobiles manufactured by General Motors in 1955. The mechanism has evolved to the steering gear shown in Figure 6. Since the 1960s, precision ball screws have been used for the feed mechanism of numerically controlled (NC) machine tools. That triggered the world-wide golden age of today's CNC machine tools.

Ball screws provide a good balance between function and cost compared with other types of linear feeding mechanisms. This characteristic and the excellent controllability provided by ball screws explains their current broad application across a variety of fields. For instance, demand for ball screws in the field of mechatronics, including semiconductors, liquid crystal displays, and robotics, is almost as high as in the machine tool industry. They are also used in special environments, such as space, aviation, and nuclear energy. This wide application of ball screws drives demand for models of increasingly higher performance.

History and Benefits of Planetary Roller Screws

The first patent for a planetary roller screw was applied for in France in 1942 by inventor Bruno Standgren. He designed a planetary roller screw and applied it to a narrow-gauge train in a coal mine in France in 1949. In 1954, he applied for the patent shown in Figure 7 in the U.S. as well. Since then, planetary roller screws have been applied to some machine tools and airplanes.

A planetary roller screw was also used in the grip of ROTEX (the world's first remote control robot) used in the space shuttle Columbia in 1993. This roller screw was developed out of necessity by the German Aerospace Center (DLR), as none of the other technologies available at the time were sufficient for the task. The planetary roller screw developed was 30 to 40 percent smaller than an equivalent ball screw, had more than 10 times longer service life, and offered higher thrust.

As with ball screws, planetary roller screws also convert the rotation of a screw shaft into precise linear motion.

Figure 7: The U.S. patent for a planetary roller screw (1954)

Ball Screws vs
Planetary Roller Screws

Ball screws have three basic functions:

Motion conversion, whereby rotary motion is converted into linear motion and vice versa;
Deceleration, where a large displacement is converted into a small displacement; and
Boosting, where a small force (torque) is converted into a large force.

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Planetary Roller screws have three basic functions:

Lightweight and compact. Do not require the deceleration mechanism that is necessary in ball screw mechanisms;
High load capacity and long service life. Generate minimum friction and heat since the rollers are separated from one another and there are many contact points; and
Maintenance of braking force. Able to maintain the braking force without electrifying the motor, which saves power

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