Optimized motor series for machine tools
Torque Motors: Machining Accuracy in the Submicrometer Range
2017-11-13 | Schweinfurt/Suhl
Through innovative optimization of the SRV IDAM torque motor series, Schaeffler has eliminated disruptive forces and torques in the motor that cause the axis or clamping surface to tilt in the micrometer range in standard rotary axis and table designs. Such tilting adversely affects the surface quality during precision machining and results in additional costs by requiring rework.
The phenomenon of short-wave surface defects can occur in workpieces when very rigid and directly-driven rotary axes are used for cutting in ultra-precise milling, grinding, and gear cutting machines. They are often detectable as visible effects on the surfaces, such as regular stripes or shadows or as grinding marks on end faces. These precision deviations of less than one micrometer to several micrometers in size lead to quality problems in high-precision workpieces in mold making, lens finishing, and top-quality gearing pieces. The deviations are caused by pulsing axial and radial forces emanating from the magnetic fields of the torque drive, producing disruptive forces and torques in bearings via a lever arm. Such relatively small loads in the bearing cause axis displacement and tilting in the submicrometer range, which may show up in the workpiece surface. Particularly with grinding marks, the error period is generally attributable to the number of poles. While the phenomenon is nothing new, today’s surface qualities are now so high that these phenomena can surface as visible machining marks. In addition, the demands on geometric tolerances and surface qualities in some industries have increased so much that the outlays for rework are no longer tolerated and the market is on the lookout for a solution.
The engineers at INA – Drives & Mechatronics AG & Co. KG (IDAM), the direct drive specialist within the Schaeffler Group, have developed the solution of a “double” motor structure, which is able to compensate for the disruptive forces and torques that occur inside the motor, in this way effectively preventing the surface flaws in ultra-precision production listed above.
Despite their more complex design, the innovative SRV torque motors based on this principle are interchangeable with normal torque motors. Air gap diameters from 89 to over 460 mm and magnetic heights from 25 to 200 mm are being planned for the new series. The series has already been launched with an installation size that has an air gap diameter of 89 mm.
Using the new SRV torque motors does not subject the machine structure to any measurable pulsing, motor-related axial and radial forces. This makes it possible now to produce the top-quality surfaces without visible flaws and with extremely high geometric and dimensional accuracy. At the same time, the new motors offer very high speeds of up to 14,000 rpm.
Publisher: Schaeffler Technologies AG & Co. KG