Guidelines for Key Technologies of ETEL LMG/LMS Linear Motor Integration

Mechanical structure stiffness and installation criteria

7.1 Clearance between rotor and stator

The magnetic attraction of the iron core motor can reach several times the rated force (such as 3000 N peak force corresponding to 4000 N magnetic attraction), which imposes a huge static load on the guide rail and mounting screws. When selecting guide rails, it is necessary to consider the combined force of the weight of the rotor, load, and magnetic attraction, and ensure that the safety factor is greater than 3. When installing the stator (magnetic circuit) on the machine bed, it is recommended to use leveling shims to control the air gap within ± 0.2 mm, otherwise it will change the magnetic field symmetry and increase thrust fluctuations.

7.2 First order frequency of the whole machine

ETEL emphasizes that the natural frequency of the structure should be higher than 200 Hz. If it is lower than this value, the gain of the position loop is limited and the dynamic response deteriorates. The cross-section of the column can be optimized through finite element analysis, or damping materials can be added. For the gantry dual drive structure, special attention should be paid to the torsional mode to avoid resonance caused by phase delay of the two axes.

Integration points in typical application cases

8.1 CMM Coordinate Measuring Machine

The CMM of AIMS and other brands adopts LMS/LMG direct drive, achieving sub micron level repeatability accuracy. Key integration details:

Using air floating bearings to eliminate friction, coupled with a suction free and iron core motor (but in this case, an iron core is used, relying on high stiffness guide rails to counteract suction).

The measurement force is extremely small, so LMG (ETEL patented slotted+fractional slot winding) with low tooth slot force design is chosen to control the low-speed (<10 mm/s) speed fluctuation within 0.05%.

Long term operation without wear and tear, with accuracy consistent with factory standards after many years, greatly reducing calibration frequency.

8.2 Flying Needle Testing Machine (SPEA)

24 axis coordinated motion, Z-axis customized motor achieves 15g acceleration. Key points:

The main X/Y axis adopts LMG, which has high force density and can quickly respond to short stroke (<50 mm) high-frequency movement.

The customized Z-axis adopts a single-phase moving magnet structure, with small volume and high thrust to weight ratio. Combined with the high bandwidth current loop of the ETEL controller, it achieves a motion resolution of 20 nm.

Thermal management: Due to the closed testing area, water-cooled substrates are used, and the coolant temperature is controlled at 22 ± 0.1 ° C to ensure long-term thermal stability.

8.3 AOI Automatic Optical Inspection

Camtek and other devices use LMG driven high-power lenses to scan PCBs. Notes:

The scanning path needs to be smooth, and the speed feedback adopts sine wave interpolation to avoid image distortion caused by sudden acceleration and deceleration.

Segmented splicing of motor stator (long stroke) requires continuous magnetic field at the splicing point, and ETEL provides tooth profile treatment with "no end effect" to eliminate peak tooth slot force at the end.

8.4 Wire bonding machine (Hesse)

The high dynamic Z-axis uses ILF+coreless technology, with a moving mass of only tens of grams and an acceleration of 30g, which can shorten the start stop time of the welding head. But there is no heat dissipation difference in the iron core, so forced air cooling is required and the duty cycle is limited to<30%. The X/Y platform uses LMS iron core to provide strong torque, combined with the ACCURET controller's "vibration suppression" filter, to eliminate residual oscillation during the wire bonding process.

Maintenance and Fault Prevention

Although the direct drive system does not require replacement of transmission components, regular inspections are still necessary

Encoder contamination: Optical glass gratings are susceptible to oil mist contamination, leading to a decrease in signal amplitude. They should be cleaned monthly with a dust-free cloth.

Magnetic circuit attracts metal shavings: The strong magnetic field of the iron core motor will attract iron powder and scratch the surface of the stator. It is recommended to install non-magnetic baffles inside the protective cover and regularly blow them with compressed air.

Cable fatigue: The dynamic drag chain cable should use high flexibility shielded wire with a bending radius greater than 10 times the wire diameter, and the insulation resistance should be checked after every million cycles.